I've got TruVativ Omnium's, so I can't move the chainring from one side to the other... and my velocity wheels w/ velocity hubs have a dura ace cog... it's all 1/8. With that knowledge, how would one go about straightening the chain line?

For that matter, how does one go about measuring the inaccuracy of the chainline in the first place? I got the cranks and wheels at the same time, and suddenly there was a buzz from the chain that has continued since... it's annoying and can't help me much.

how is the tension on that chain?
i would guess you would have to adjust something in the wheel...spacers?

tension is good and consistent around the chain ring.

It just makes sense that the chain line is off. Looking down from above the chain, the chain is catching the top of my chain ring with the chain being towards the bike... there is a small gap of course, and the chain is getting pulled away from the frame, so to speak.
When the bottom of the cog grabs the chain, it is pulling it back towards the bike. I'd say there is a barely noticeable crooked chain line

I read a lot about 42.5mm chain lines, etc. How is that measured?

Is there a good measuring tool that is inexpensive? Thanks!

Ruler's are cheap and it is measured from the center of the downtube to the chainring. In most cases you're gonna be looking for a 42mm chainline.

https://www.sheldonbrown.com/gloss_ch.html#chainline

there is also a chart for chain line with different cog/hub combinations.