I would say it's more of a fundraising thing. These college programs are able to fund raise to pay the athletes way more than the OTC could. In essence, there are a lot more college wrestling alumni that are willing to donate back to their program than there are people donating to the senior level athletes at the OTC. Some say that USA Wrestling isn't funneling the funds in the right direction, but that's a whole different discussion.
In terms of the fairness, I actually think there are NCAA rules about keeping the RTC separate. However, it seems like these rules are kind of vauge, interpreted differently, and not really enforced. For the most part, these schools have separate RTC practices than their normal practice time so the college athletes can choose to go these practices to work with the RTC athletes on their own. So, it's not exactly like you said about the RTC athletes practicing with them, but at the same time, different colleges seem to interpret the rule differently as well.
It's an interesting topic for sure! I think the RTCs have done a lot to help wrestling, so I'm in favor of them. Think about how many more guys are still wrestling and trying to make the Olympics compared to 10-12 years ago. I think this is in big part due to the RTCs and the Living The Dream Fund. Even if it does create a bit of an advantage for some schools, it seems to be beneficial for wrestling in the big picture, in my opinion.