Please don't let your mind get too worked up about your upcoming root canal. I don't think you have anything to worry about with your hip. As sharon said.....if the correlation between dental infections and an infected joint were that profound, we'd all be in trouble!
Any correlation has just been a supposition. There have been no studies that point to the possibility of an infected joint resulting from an oral infection. More and more medical professionals are backing off from the idea that one needs antibiotics for routine procedures such as cleanings and root canals. Our body is a wonderous machine that fights infections very well under most conditions.
I can tell you a personal story that may ease your mind. I learned about 6 weeks after my TKR that I probably had an infected tooth for some period of time BEFORE the surgery. Unfortunately the problem could not be easily seen on xrays and it was not discovered in my pre-surgery dental checkup. Shortly after surgery, I began to notice pain in this one tooth. But I decided to wait to see anyone about it until my 6-week checkup with my surgeon. By then, my tooth was fairly painful and I thought I could feel an area of decay at the root level. I was okayed at 6 weeks for dental work and made an appointment with my dentist. The problem was STILL difficult to see on xray, but careful examination by her and an endodontist revealed a pus pocket at the base of the root and a tooth that was in "resorption" (basically destroying itself). Root canal was done and it was a doosie. I've seen a couple of them done with virtually no problem for the patient. Not so with me, probably because my problem had been brewing for so long. But the root canal was done and a crown placed. That was about 4 months ago. I'm happy to report both tooth and knees are just fine. I just had checkups with my surgeon, my dentist and the endodontist that confirmed all looks good.
So....try to relax. Congratulate yourself that you have discovered this quickly and are taking action. My feeling is that you're going to be just fine once the tooth problem is taken care of.