I've contacted YETI CYCLES info and they have answered me:
"Unfortunately I've searched, and we don't have the information for the oil levels on that shock at this point. I'll email a couple of our guys that have been here from the beginning to see if I can get more information on this, but I have a feeling that one may end up being trial and error as of now. Sorry I can give you any more information on this one at the moment, but please let us know if we can help with anything else. Thanks."
5w IIRC.
Once the shock is apart and on the bench, work on a tray. Fill the can the whole way up with oil, then put the piston in. It'll spill over into the tray. Idea is to get as much air out as possible.
I have found out that the shock absorbers were manufactured by "Risse Racing" and that the model is the "Genesis", very similar also to the "Fox Alps".
Complete maintenance is explained in this video. 5 weight oil, to the bottom of the thread.