Ignoring whether or not a fully insured plan is appropriate or not for their situation...
Off the cuff, yes, presumably you can do one. As for RMD's, you are going to calculate an annuity based upon the benefit, right? In essence no different than a traditional DB, other than how you arrive at the appropriate benefit, (I think.) As to taxable term costs, if they are unincorporated partners, they can neither deduct the TTC, nor can they recover it as basis later. Perhaps you can delay the effect a bit by using cliff vesting? Remember, you can't roll over the RMD's, so I guess you'd have to crunch some numbers to determine if all this fol-de-rol will ultimately be worth it. They might possibly be better off with a 401(k) and employer discretionary, and max themselves out, with catchups? Andy's opinion on that will be far more informed than mine in terms of potential numbers! Plus he's a Bosox fan, which makes him a fine, informed, trustworthy, intelligent person, as opposed to those who root for the Evil Empire, and are therefore pond scum.
Sorry, I can't help myself - baseball is in the air, so the world will soon be right again.
I see SoCal addressed some of the questions while I was typing this.