It's easy if you're a guy.....if you get a hard-on while tickling or get tickled by someone, it's WRONG! 🙂
Except it's not always that simple - it isn't necessarily the tickling causing it. Hypothetically speaking, say a couple of fairly attractive girls pinned a guy down with intent to tickle him for whatever reason, he might be turned on by the girls pinning him down as opposed to the tickling. In this eventuality, how can you blame the guy - noting it may not be totally consensual?
Anyway. In response to the original thread questions.
Is it ok to get people to tickle you unawares of what your fetish is?
Depends on the situation. "Is it OK to get people to tickle you in such a way you're getting off on it" is totally different to "is it OK to get into a playful tickle fight or something with someone."
Is tickling always sexual to you or is it innocently playful between friends?
Not always sexual - I can easily differentiate between the two forms. While yes, in some situations it IS sexual, in others it's a simple bonding activity.
Does it matter more how you view it or how they might if they knew?
Assuming the person in question is finding it sexual: it matters, to be honest, more of the fetishist views it.
"Ignorance is bliss", does it matter if its not hurting anyone?
To some extent, yes. To some, no. Again, in the case of spontaneous tickling between friends, it's hard to say - I mean, saying "stop" won't necessarily accomplish anything, while saying "stop, seriously, this is a huge turnon" could get just as bad as the person finding out in another way. Depends how long it's likely to last, I suppose.
Really, it depends on the people involved. Assuming someone can differentiate between sexual and non-sexual tickling, and doesn't class something as sexual, then it's OK. Sure, it might still be a lot of fun, but in a different way - just because you have a kink, doesn't mean that that action will always turn you on or whatever.
However, if someone is deliberately using someone who doesn't know for their own sexual aggrandisement, then it's wrong. End of. The tricky bit is determining what is "deliberate..."