It all depends on what type of site it is, if its an indoor CQB then you're not likely to have a sniper playing.It's the same argument you could have with the ghillie suit in general. It's not as if it's something that only im allowed to wear.
I've never seen any none ghillie wear it on their leg and I wonder if the site owners would have any issue with that?
But as a counter question, what about some of the sites that operate bands Vs none bands? Is one team cheating?
And also, (sorry for the incoherent format of this reply, just woken up after a night shift), what's the purpose of the band? To denote who's team your on or to make you stand out? Because as some of the replies to this topic would suggest, they're sole purpose is to make you stand out should you be trying to be sneaky and hide from the enemy team.
If there are sites that operate outdoor games where you have banded and non-banded and Mr Ghillie suit wearer decided to conceal their armbands by wearing them on their ankles... it presents an unfair advantage because you don't know if that is a team member or not.
Simply put, if you have two teams and one wears armbands then that is where they must be worn.