Being treated for a yeast infection on arm. can i sleep in the same bed as my wife?

Little or no risk: Maybe a non-yeast fungal infection. (Yeast is a type of fungus, but other fungus types usually cause non-genital skin infections.) Not eastily transmitted to others. And the fungus maybe present for months before rash started, so your wife has already been repeatedly exposed. Probably no point in changing sleep arrangements at this time. Check with the doctor treating you if you remain in doubt.