The impression I got was that Kitty had a distaste for using actual sex (rather then promised sex) to get money, but that she had done it before in the past, most likely forced to by Johnny. So in the past she has acted as a prostitute and Johnny her pimp, but it's not either of their regular occupation. You get the impression if Johnny wants money, he'll get it and he's shown he's not concerned about other people having sex with Kitty if it get's him his cash. I would be suprised if he'd never pimped her out before, but as a regular thing? Nah
Yes, he hustles a little here and there, but remember when she states that she's given him a total of $900 over a course of time, and that she's still waiting for him to buy her a ring with that money?
"Lang had to rely on little queues like this, because he was forbidden, by the production code to call Kitty a prostitute outright. He had to find subtle ways of singnaling that fact to the attentive viewer, without outraging the censors."