Apparently Rogan is an co-investor in a competitor of MSLP...Onnit. TJ Dillashaw is (was?) signed to them. Rogan has had guest come on to talk shit about MSLP and promote Onnit, but he himself can't do it due to his ties with UFC. With TJ leaving for MSLP, I'm guessing he's not a fan of the move.
He's mentioned MSLP quite a few times in the past...never in a positive light though.