QIf I attack an enemy leader with this follower, can I play its UB Strike ability? Will it count as executed?

AYes, and yes.

QIf I move an evolved enemy follower into the EX area with this follower's UB Follower Strike ability, do both the unevolved and evolved cards get put into the EX area?

ANo. When an evolved follower is put into the EX area, only the unevolved form stays in the EX area. The evolved follower is moved faceup to the evolve deck area.

QIf I put a follower into the EX area with this follower's UB Follower Strike ability, does it lose any damage dealt or abilities given to it?

AYes, it does.

QIf I put an enemy advanced follower into the EX area with this follower's UB Follower Strike ability, does it get put into it's owner's evolve deck faceup?

ANo. It remains in its owner's EX area after you put it there. Advanced followers may exist in the evolve deck, field, EX area, and resolution zone. They are only moved to the owner's evolve deck and placed faceup immediately after movement to other zones.

QIf I put an enemy token follower into the EX area with this follower's UB Follower Strike ability, does it get removed from the game?

ANo. It remains in its owner's EX area after you put it there. Follower and amulet tokens may exist in the EX area, field, and resolution zone. They are only removed from the game immediately after movement to other zones.

QIf my opponent's EX area is full, can I still put the attack target into it?

ANo. It would remain on the field.