But I can't quite put my finger on what this tree is:
I've seen it before, seems to be tropical, compound leaf with 5-9 leaflets. For reference regarding the bark the tree pictured is over 30 years as a bonsai according to its owner.
I just looked at your link and a few other photos and I think you got it. Funny, the owner said it had never flowered, but perhaps it wouldn't with 30 years of no fertilizer.
I thought the leaves resemble that of Rose of Sharon. I wiped them out in my landscape years ago so cannot recall exactly what the trunk part looked like.