Will a Shimano 10 speed cassette fit and work on a Shimano 9 speed hub?

https://www.drivetraincalculator.com/drivetrain.php?A useful link but not seeing a hub option ?

While you're waiting for a practical expert to chime in, this from Shimano might help:

In most cases you can use a 10-speed cassette on a 9-speed hub except in the following combination's:

• CS-7800/6600/5600 gear combination's 11/21, 11/23, 12/21, 12/23 cannot be used on WH-6500 and WH-7700 wheels.

• CS-7800 gear combination 11/21 cannot be used on WH-R540 wheels.

• WH-R535 wheels cannot accept any 10-speed cassettes.

NOTE: When installing the CS-7800/6600/5600 on a 9-speed freehub, you must use the supplied 1mm spacer (part# Y1Z807000) behind the cassette to space the gear properly in the frame.

https://www.shimano.com/publish/conte...faqs_0003.html

10 spd S cassettes will fit on any hub I'm aware of that is designed for 8,9, or 10 spd S. You will usually need a 1mm spacer installed before the cassette. This spacer is supplied with the cassette.

There must be some other strange reason why some Shimano *wheels* aren't compatible with all gear ratios...

Just to be precise, what Shimano hub are you seeking to use a 10 speed cassette with?

I am hoping that these Ultegra 9 speed hubs...



...will work with my Felt hubbed 10 speed cassette..?

I'd say "yup" with the possible difficulty of an 11 tooth gear on an older hub. From the late great Master Brown:
https://sheldonbrown.com/speeds.html

Shimano Freehub Cassette Systems (and copies)
In general, all Shimano Cassette Freehubs will work with all Shimano cassettes, any number of speeds. There are a very few exceptions:

7-speed hubs won't normally accept 8-, 9- or 10 speed cassettes without modification. Click here for details.
7-speed cassettes fit fine on 8- and 9-speed (and most 10-speed) hubs if you put a 4.5 mm spacer onto the body before the cassette. Click here for details.
Older "Uniglide" Freehubs (including all 6-speed units) won't accept modern cassettes without modification. The last Uniglide Freehubs were made in the 1989 model year. Click here for details.

These older hubs can usually be upgraded to work with modern Hyperglide cassettes by replacing the Freehub body. Click here for details.
Some Freehubs are not designed to accommodate cassettes that include an 11 tooth sprocket. Click here for details.
2004-2007 Dura-Ace hubs with aluminum Freehub bodies won't work with anything but 10-speed cassettes. Click here for details.
Capreo hubs and cassettes (with the 9-tooth smallest sprocket) only work together. Click here for details.

Sorry about the nonfunctioning links, but you can see the original site. As to th e11 speed on an older hub problem:
https://sheldonbrown.com/k7.html#hyperdrivec
"Hyperglide-C" cassettes on conventional bodies.

A wobbly cassette may result from a loose lockring, or wear of an early Uniglide hub, but there is another potential cause.

Shimano uses the trademark "Hyperglide-C" to designate a system with an 11 tooth sprocket. The "C" stands for "compact". These systems are used with smaller-than-usual chainwheel sizes, or on bicycles that have a small drive wheel, or to achieve higher gears.

Due to clearance problems, the cutaway between the splines on 11-tooth sprockets only goes halfway through the sprocket. The matching splines on Hyperglide-C bodies don't go all the way to the outer end of the body.
bicycle cassette freehub freewheel derailleur derailer shimano index sprocket cog cassette freehub hyperglide 7-speed 8-speed 9-speed uniglide freewheel ultegra Dura-Ace exage acera alivio hyperdrive bent axle bicycles sheldon brown capt bike captbike captain
Hyperglide "C" body Non-compact body
If you install a cassette with an 11 tooth sprocket on an older, non-compact body, the cassette will not be properly secured, and the sprockets (other than the 11) will be loose and wobbly.

There are two ways around this problem:

You can use Hyperglide-C cassettes on conventional bodies by adding a 1 mm thick spacer to the body before installing the cassette. This is a standard spacer commonly used for fine-tuning chainline with conventional freewheels. It may be necessary to add a spacer to the right side of the axle in some applications, especially if you wish to make the wheel interchange with other wheels without needing to re-adjust the rear derailer.
Alternately, you can grind a bevel on the ends of the splines of an older body. This is a five-minute job if you have access to a bench grinder. Clean up carefully afterward so particles of metal and grinding-wheel grit don't wear out the bearings.

Note, if you install an 11-tooth sprocket on an existing cassette that had a larger top gear, you must also replace the Hyperglide lockring with a Hyperglide-C lockring. The lockrings made to work with 11-tooth sprockets have a smaller outside diameter. If you use a larger lockring, the side plates of the chain will hit the edge of the lockring, and the chain will not run properly on the 11-tooth sprocket. (Hyperglide-C lockrings are compatible with 12-tooth sprockets though not always with larger ones.)