You can accept cash donations from geni. You cannot have a guarantor member called "geni".
True, if we want to give some form of membership to people that want to completely hide their real names we would need a less official type of member. However, while guarantor members real names do need to be made available to the public on request, there is no need to link those names to pseudonyms - pseudonyms can be kept private. Someone could go through the list of names and try and work out by a process of elimination who you are, but I think they would struggle, at least once the list of members gets reasonably large. Also, we don't have to give membership to every donor, people can just donate money and then that's the end of our relationship with them.
If we are going to have a less official form of member I suggest not using the word "member" to avoid confusion, "friend" is better.