To sum it all up, the answer to the question Does PokerStars allow HUD?  is, yes. But there are some conditions that you have to strictly follow.

- Restart HM3 and ensure HM3 and the HM3 Server (Auto Import/HUD) are fully started. - Launch your poker client(s). If you continue to have problems: Make sure you always start HM3 first before you open the PokerStars Client.