Yes. Say the rays are too thin that they become overly floppy. Some prefer a more sturdy fin. So they cross to a PK and work them selves back to VT . . . of what ever form they are working on. Since spade shaped caudal is desired (I think), try to look for a PK with rather spade shaped caudal. Hopefully you will get spade shaped VT somewhere along your line.
Color too is a goal you can achieve by crossing. Say there are no dragon scaled VT in your area, but there are lots of dragon scaled HM or PK.
What is important to consider when thinking of cross breeding fin type is your goal. Will the cross compliment your goal? So don't just cross them without reason other than availability (if possible).