Welcome to Nikonites.
I've seen plenty of wedding photographers bouncing around with nothing but cropped sensor cameras, and while many of them were far from what I'd call "professional", suffice it to say that it goes to show you that knowing how to use what's in your hands is far more important than having a specific something in your hands - 9 times out of 10.
If I were to require a portrait photographer chances are the first thing I ask them is not going to be, "What kind of camera do you use?", but rather, "Can I see your portfolio?". If I'm impressed enough to hire them after that, I may ask them, as a photographer, "Just curious, what do you shoot with?". If they were to tell me, "Nikon D60", I might look at them funny before saying, "Damn, that's pretty impressive stuff from an old cropped sensor!!", and then book a sitting. It's about your work, not your camera. The only people that might shy away are people who think they know about photography, which is 75% of the people you meet in ever photography club. They're nice people, well intentioned, but like all gear heads, it's about what you're carrying, not what comes out of it. I see the same thing in guitar forums. "That guy's badass!! That's a PRS Artist Series with a 10+ top from Paul's Private Reserve stash!! He met Paul at a bar, got a personal factory tour and got to pick the top himself!!!" Unfortunately, he plays worse than I do, and that's saying something. LOL (guitar players will understand this)
So, to a specific answer, you sure as heck can make a living as a portrait photographer with a D7100 if you have the other skills and tools to go with it. If you think it's a factor, take a little black gaffer tape and cover both the "Nikon" and the model number on all your cameras. Now only the insanely curious will ask, and if they walk out on you after you tell them at least you can keep their booking deposit, and save yourself the trouble of dealing with their complaints afterwards since they're also probably the type to pick nits on everything.