I know this is a touchy subject for a lot of people, and I mean no disrespect to anyone. I just wanted to preface my reply with that!
I think tarot cards should not be used. Let's be honest, the only reason you asked about this is because you realized that some people could take the use of tarot cards religiously. If you did not think there was a religious connection, it wouldn't even be a question. I'm a firm believer in the "better safe than sorry" method when it comes to this rule. If you think something is part of a religion, don't use it in-game.
For example, I thought it would be cool to give my character a cross-shaped scar. But you know what? I'm not doing it because it's possible that someone could take it offensively, and the whole point of the game is that everyone can be included and not have to worry about being offended. In-game we avoid religion, real racism, and sexual assault for that reason. All characters are created equal!
(Well, kinda. You know what I mean!
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I just don't think it's fair to not allow major religious symbols while saying other things are okay. It would freak me out if someone tried reading tarot on my character. I would, at the very least, go out-of-game and ask them to stop. (The cards don't know you're in-game. They're reading your out-of-game fortune.) And it doesn't matter if people agree about it or not. The point is that, to some people, tarot is real and religious. Whether people like it or dislike it, it's better to just not offend someone.
Besides, there are other methods of fortune telling that are obviously fake that you can use. Make something up. Spin around in a circle and hum. Put your palm out in front of someone's face and touch your temple with your other hand. Jump around in the dirt while singing the character's name then inspect your footprints. Or even make a set of ten fake cards and put a triangle on one, a squiggle on the second, a circle on the third, etc. I mean, really. This is LARP. We're acting. It's not MEANT to be real.
No one is saying don't be a fortune teller. Just do it in a way that does not use methods of fortune telling that exist in reality.
(Also, if someone asked me not to wear a sun on my armor because they worship Ra, I would change my armor. Just saying.)