I practice my rudiments with just about every type of stick I have in my bag. From 7A's through to 5A's/5B's through to 3A's or 2B's.....and from time to time, I break out the marching sticks for a giggle.
I've never noticed any detrimental effects from using tree trunks....but that said, I'm not sold on the fact that they help any more than any other stick I use either. My hands play the rudiments...not my sticks. But at the same time, I like that I can go from one stick to another with no discomfort and only a little adjustment period too.
Just further on jakesters comment "it will help your muscles because they are a heavier stick when u use drum set sticks your be better". Whilst I think there is an element of truth in this......personally I've found that the heavier stick also promotes more rebound (especially off a pad) and this somewhat negates how hard you're actually working your muscles. When I want to blaze away and get some muscle "burn"....I'll often opt for a smaller lighter stick to do it with. YMMV, but something to think about.