Li's right. I actually asked the hotel I was last SC and they gave me that exact reason. Truth is, Unless you go upstairs at night, with more then 4 people, they'll never notice....We had all 4 people in the room after like 10pm and one of the guys had his gf in there for a good hour or 2 and no one even saw her come in..They would have never even known she was there..They are more preoccupied with room parties and other annoyances that some con goers bring (like being wasted and making tons of noise or something).
I would call anyway just to be on the safe side, then if they say it's ok, then I guess no worries, but if not, Just go ahead, it's only ONE person..
On a side note, some photels have an extras cot that they will bring into the room (some are in the room, depends on hotel) specifically for a 5th person.
Cosplay DA Regular DA
Kumoricon 2014 (so far):
-Sora (Kingdom Hearts 2)
-Alice (Hearts no Kuni no Alice)
-Black&Blue Loli-style Dark Magical Girl O.C.
-Akaito (Vocaloid. Black & Red Ver.)
Dream cosplays for now:
-Tsuruya-san (Haruhi Suzumiya)
-Kagami Hiiragi (Lucky Star)