Honestly, I have NEVER seen or heard anything about a Scottish war drum made from a huge tree.
I'm from Scotland and I actually studied Scottish history and Scottish Music and the like. I've never come across anything like it.
Before marching drums came about the thing most used was a large bodhran which still wouldn't involve a giant tree.

I'm a fan of Saor Patrol, but I wonder if they were pulling someone's leg.
As an alternative to a drum like that, I'd say go ahead and build yourself a bodhran.