As a San Diegan, I can say that the impression of the local LGBT community is that Carl is anything but a 'good guy' when it comes to politics.
As another San Diegan, I'll second that. He has a reputation as a tyrant from his days as a city council member.
You'd think the local LGBT community would rally behind one of their own, but I've never seen any evidence that he rallied behind us. During the Prop 8 campaign, he was silent and the only Republican in the city who stood up for marriage equality was Mayor Sanders. (Mayor-elect Faulconer's position only changed when public opinion shifted in the years after Prop 8.)
During DeMaio's failed mayoral campaign in 2012, he downplayed (but never denied, at least) his sexual orientation and would quickly move on when it was brought up. With his reputation as a fiscal conservative, he could be that unicorn candidate who appeals to moderates who dislike the religious right aspects of GOP social politics, but the commercial above is only the first time he's ever shown himself as anything but a lock-step Republican.
With the stink of his loss to Bob Filner still on him, he'll have to come up with a compelling reason for people to vote against Peters. It's a battle for the middle with more independent voters in that congressional district than either of the two parties and DeMaio could lose a few of his base votes simply because he's gay.