I've done these both ways with success. That said, the two possible negatives to printing first are
1. If the white ink layer is not consistently sufficient, dye could sneak in where it's weak
2. With some tying techniques, it could be a little bit tougher to get a really tight tie where there is plastisol.
As I said though, the times that I have done it this way, it apparently worked fine as there were no complaints.
And, btw, I have never had bleeding with properly done procion dyes.