Prolly. I would talk to a Alienware Tech Support Represenative about the reasons you feel you need to apply artic silver 5. Most of the time alienware will only allow the "Dow Corning" gel. Then again, that was with my m7700 I was told this, so it could be a m7700 specific gel.
I would defenatly talk to a rep about your overheating problems and try to get it fixed, normally artic silver is uses to lower only a few degrees. If you have heat issues, it could be something else.