Can I use a Suntour Cyclone GT Rear Derailleur for a 10 speed Campagnolo cassette?
Campagnolo 10 speed cassette is only 0.6mm wider end-to-end than their 9-speed cassette, so as long as the 9-speed setup still has that much adjustment in the limit screws you should be fine on that count.

The jockey wheels only care about the inside width of the chain which is 3/32" on pretty-much all derailleur gear systems that have ever existed, so you won't need to change them for that reason.

I would try it, if it doesn't work you can always fall back to your 9-speed plan.