An awesome 기사 I found on LJ that uses a compilation of interview evidence which shows why Castiel's loyalty is not an issue. No spoilers beyond aired episodes in Season 5.
From Supernaturalwiki:Cosplay - dressing as characters in the show - has been a minor but creative part of the fandom. Press on the red 링그 so 당신 can see some hilarious pics of 팬 dressed up as SPN characters!!