Note: For those who doesn't want to read my entire rant, just skip to the bold green text.
Well, in SL we have Vampire Lord Baluski and his beautiful bride haunting the forest. There are also Gorgons and Werewolves. So in other words, SL is based on Naruto, and not 100% Naruto Universe. Thus demon, angel, vampires, werewolves and other super natural creatures should be consider legit on SL in terms of roleplaying.
But there is a community of roleplayers here who RP Naruto on SL in a hardcore kind of way. To them such beings do not exist, and when they are faced with one...well...it's alien to them and simply beyond their comprehension. They reject it because they are unable to translate those foreign powers into Naruto terms. Some extremely hardcore roleplayers would even go as far as to reject anything (Jutsu, KG, techniques etc) that are not shown in the manga.
I personally, is the kind of guy who embrace creativity. So as long as a player does a good job at relating their powers to Naruto, it's consider legit and acceptable in my eyes. Such as vampires as a clan characteristic, werewolves being an advance form of Kiba's clan technique, demonic powers as some sort of KG or Senjutsu-level technique.
However, I'm also a person who doesn't push my own perceptions onto others. So for example, if I were to join the community of extremely hardcore roleplayers, I would go by their rules and drop my Reiton (Soul Release) without any complaints.
To sum it up, every roleplaying community has their own rules. You'll have to go by their rules if you want to join them. Those rules aren't meant to push their perception upon you, but to regulate the RP in their own community. There maybe a few who would force their perception onto others, but please don't judge the whole community just because of a few who went a little too far when enforcing their own rules.