I know beta providing has been observed in baboons. In Baboon troops, you have an alpha male who gets exclusive breeding rights with all the females, beta males are allowed to hang around. The alpha doesn't have much time to spend with each baboon roastie though, so the beta males will spend time with them and share their food with them. The females will then sneak off with the beta males and sleep with them behind the alphas back. This is to keep the beta around to care for any babies in the future. It is hard to say who is getting cucked in the scenario though, since the beta does actually get breeding access so there is a chance the offspring will be his. I suppose if the alpha has that many females loyal to him, the odds improve for the beta as the alpha is spread thin across to many females.