IS there a difference in a 3 under release?
If you mean, is the '3 under' release executed differently than a 'split finger' release. the answer is no.
What could change is the pressure applied to the string by the individual fingers, now that the index finger is no longer isolated above the nock. As you're probably aware, a change in the pressure of individual fingers can cause differences in arrow flight and impact point. That's one of the little challenges that keep trad archery so interesting! IMHO.
Have Fun!