I see a lot of huds have a target reticule for the alien team. Wouldn't that be considered cheating since the aliens originally have no reticules?
People debated that quite a lot when those huds first came out. It's not really an easy question to answer, but certainly they may be used and discussed and traded freely on these forums. Servers have no way to tell if you are or are not using them.
1.2 alien hud simply has the crosshairs to avoid the issue entirely.