I have a questions.
Is this a bug?
It's definitely a new interaction from the new curse/reanimation types and the lycanthropy curse. That doesn't sound like a bug to me, it sounds awesome!
Was my cursed corpse already a waretapir before it died?
Did my cursed corpse contract lycanthropy from the other waretapirs?
I think you'd have to do some Science to see in what order those effects can be applied. Might be hard to tell after the fact.
Is this normal?
Let's hope so!!!!
Is there a way to deal with OP creatures like this, or is this just Dwarf Fortress normal behavior?
I'm not sure from your description if this is really OP. How skilled and equipped were the military? Were the fights mostly quick 1:1, or did it stand up well to several skilled attackers at once? How often was it hit, and with what weapon types? Did it stay effective after losing limbs? Is it vulnerable to bisection? Does it have a thought center that can be crushed? Did the lycanthropic change regenerate lost parts? What happened when it was filled with bolts?
Note that all of the above questions don't invoke anything beyond simple military defenses, like bridges, magma-based defenses, siege weapons, things falling long distances, or the wonderful world of high speed minecarts.
In DF, there's ALWAYS a way to deal with an attacker. (Except maybe if there's new noncorporeal ghost-type enemies that ignore tile changes? Haven't heard of anything like that yet, though.)