This is a young guy putting in the work to make it in MMA legitimately though. He comes into the UFC with massive drawing power, the kind that can't even be matched by some phenomenal rookie with 10 straight KO's.
He's not Randy Couture fighting another has-been for one last glory ride. Guys like Rock, and other part timers, have been there and done that in WWE. Punk's problem was never with their participation, it was with their execution. Rock, Taker, Brock, HHH, Sting, other part timers could be used to catapult young talent to the stratosphere. The way Rollins beat Sting, Lesnar once best Hogan then Rock.
Punk's issue was that he would get pinned by Taker one night, while someone else eats Rocks pin, then the next night the two Mania losers would be the biggest stars in the company and have to rebuild their credibility.
Everyone wants to get the low hanging, reactionary fruit of "Punk is stealing a spot in MMA, he's mad that stars steal spots in wrestling!" But in as many ways as the UFC & WWE are similar, they're also significantly different.
Unless those Punk critics believe that he despised the Lawler/Kaufman stuff. If the WWE landed Rhonda Rousey for some mainstream excitement, she wouldn't be signed to have a 5 star match. She'd be signed for the spectacle. It all comes down to execution like I mentioned. In that scenario don't have Rousey squash Charlotte, your women's champ, but there are great uses for her. The same way you shouldn't have Rock come in for 2 months between movies and kill off a strong run, or flatten a Wyatt in seconds.
Anyone can love or hate CM Punk as much as they want, but saying he's a hypocrite for his WWE criticism/UFC deal is a misguided reason.