I dont think it breaks stealth but I typically have to get quite close as I usually will try to keep one of the more dangerous mobs out of the fight. After you use the mind maze the other mobs in group will be more alerted and I think they will more easily spot me, but could be wrong here. There might be better tactics of using this skill. I havent tested every approch yet, but it might be more wise to go for a mob in the edge of the group and not in the middle, but as I mentioned you typically want to disable one of the stronger mobs. There is also a skill to increase my stealth level, might be possible to stay hidden closer to a group if I use that, but have not tested this extensivly. As I said I am quite new to games like this and after reading your guide wondered how to best apply my character in groups. So far I have been going mostly solo, but tried a few groups for some heroics and one flashpoint.