This _shouldn't_ work very well, because the Campy NR/SR/etc (= _not_ early Rally) design leaves a lot of space between the upper/guide pulley and the cogs. You went/need a rigid pulley up top to help guide the chain to adjacent cogs, especially with vintage freewheels that don't have fancy tooth profiles for improved shifting.
As noted above, you could swap positions, with the floating pulley below as the tension pulley, and the rigid up up top as the guide pulley. That should work OK, no real harm, or benefit that I can think of, having a floating tension pulley. But it wouldn't make sense if you were buying a new pulley set, no need to pay extra for a floating pulley you don't really need.
The reason the floating guide pulley works so well with your Ultegra 9spd rder/5spd freewheel setup is the imho superior geometry of the Ultegra, which keeps that guide pulley closer to the cog teeth, regardless of cog size. If you used a rigid guide pulley instead, you might get _slightly_ faster shifting, because your 5spd teeth aren't shaped/profiled (I'm assuming), but any der/cog misalignment would be noisier.
The floating pulley was designed for indexed shifting use, with the teeth very heavily shaped/profiled to move the chain, rather than relying on the guide pulley for precise positioning. The float keeps everything quiet if there's some minor misaligment. That becomes more important when you're shifting 7-8-9-10-11spd clusters.
Makes sense except you missed on piece on the setup on the Orbea I was talking about with that Ultegra 9 Speed RD. I'm using it with a modern 10 speed cassette not a 5 speed.
Sounds like I need to play with the Victory setup until I find the sweetspot. Right now it's running over an older 7 speed cassette. Think I'll try and modern 8 speed with shaped teeth on it after I sort out a good service on the RD. I've got various pulley's I can try on it as well as a set of the Velo Orange's coming in. Actually hope they work well with it since they look like they'll match the color of the bike, LOL!