Methinks ventral fin will be under some static load, but only limited dynamic load during the manoeuvre. The snap roll will put the fin under greather dynamic load (which may be what is needed to ruin your entire day).
Have encountered aircraft that may fly knife but are problematic in snap rolls - or at least requires mods to both stabilizer and fin to be approved to do snaps.
One thing to worry about is oil supply, though. Unless you have an inverted oil system, limit knife flight time to.... not much
.
Enjoy!