User blog comment:Martialmaniac/Ten - Is it worth mentioning?/@comment-48285-20180417181148

I would agree that we should only mention the control of Ten if it's stated in the manga. Since we don't know a lot of Nen users' capabilities, we have no way of knowing if they sustain Ten or activate it at various times or whatever. However, I think it is safe to assume that everyone that knows how to use Nen (not learning Nen), would know Ten.

As for Ren, I don't believe it was ever stated out right that it was a prerequisite for getting into Greed Island. I think that was something that Tsezguerra, a seasoned Hunter and player of Greed Island, decided on himself. We know that everyone that got in from Gon and Killua's group have a strong Ren/Hatsu (which ever one they used, something I'll touch on later) so that's something we could mention for them. As for everyone else, we don't know if they even know Ren, since we don't know who Tsezguerra judged. Also, we're not sure if the ones who passed in Gon and Killua's group showed their Ren or their Hatsu. They might have been like Gon and Killua: thought their Ren wouldn't cut it so they decided to come up with something else.

My point is: We don't know about anybody else other than those that the manga has focused on so it's all going to just be assumptions without any sources to back up the claims.