No, these should not carry the same penalties. HOWEVER, I have lived among those in San Francisco who work tirelessly to make prostitution "legal" (and of any age group wishing to engage in the profession). In their worldview, both cases you posited would be treated as the same "rape"; but the one with the prostitute would carry a heavier penalty, as in their worldview, a prostitute is not only raped but as an "official" business, she has been additionally "thefted" from.
In the case of the rapist dragging a "non-professional" -- an innocent woman walking by; they'd argue this is just "rape".
Yes, I've lived in "looney city". They also advocate that prostitutes should receive minimum wage and universal health care.
I've round-about answered yours. :P) Your cases beg other questions before they can be adequately addressed. And yes, I see another leg of the liberal platform quietly arising in background.
I am not for the legalization of prostitution. The legalization of prostitution will, in fact, serve to repeal all rape penalty/punishment laws, long-term.
You've raised the thorny point, of this matter in thise case, nonetheless. As it lays, currently: assault and battery but not rape. By her tacit "consent" to engage in sexual activity (so it appears, at anon) as a BUSINESS transaction, it comes down to assault and battery; but not rape. Rape is "carnal knowledge of a woman without her consent". I believe that is still the legal definition. In this particular case, on just how the he said/she said seems to be happening, she consented. And money appears to have changed hands.
This is very different from being dragged into an alley.
I think you are on the right track- I think that the rape of a prostitute by a john as theft rather than rape implicitly makes prostitution legal, as you would have to argue that an legal contractual obligation was formed that constituted consent. I would argue that even lowering it to assault would do the same thing.
Now how a jury sees rape of a prostitute vs. rape of an innocent stranger is another thing. Many would only give the maximum sentence in the latter case.