Actually, why would it be a problem for the tower damage giving Rook mana, it's only for 10 seconds so whoop-de-do. The amount of mana you get back is irrelevent, TB can go from 900 mana -> full in 1 Rain of Ice cast with BotS so why can't Rook get credit for HIS towers?
Also, for the UB question, you do get mana over time for the DoT effect of Spit. I've tried it and confirmed.
I think they also need to look at TB's Fire Nova and why it doesn't give you full credit for the damage you do. I've noticed that if I'm at like 50% mana with TB and click BotS and use Fire Nova on a group of creeps I don't get 75% of the damage back in mana. I see all these numbers for damage popping up around totalling up over 4k me but my mana is still only ~50% full..