There are differant oppinions on wether or not humidity does anything to help a molt. As far as that goes, do what you think the T needs. Misting definitly wont hurt. I do it for my slings and young T's. It is well known that the most important element of the molting process that is a must is the T's water intake. Internal moisture helps with the separation of the old exoskeleton and the new.
It depends on what you have. Misting a G. rosea, ever, isn't going to do anything but upset the poor animal. Even with Ts that do love humidity, you never want to mist them directly (ie, mist the enclosure, not the spider).