Should I thaw cherries for a sour cream cherry pie?
Thaw and drain them.

If you use fruit as a main ingredient like for a [your choice of fruit]pie, using frozen cherries will cause two things to happen:


They will significantly increase your baking time, because you need extra oven heat to thaw them. This may cause your crust and cream mixture to dry out or overbake.  
They will exude a lot if liquid which can 


throw the filling-to-binder (eggs, starch) ratio, causing problems with the pie setting or the filling falling apart and
cause soggy spots both in the cream filling and the crust. And mushy crust in a pie is pretty yuck.



Note that there are cases where using frozen fruit is fine, but that's typically recipes like blueberry muffins, where you add just a comparatively small amount mixed into a batter and local slightly damper spots aren't much of a problem.