Currently a practicing RT with a BS and struggling between either MD or PA route, but I've known plenty of people who have prepared/matriculated/completed med school after RT programs. Doing a BS RT program while taking pre-med classes and preparing for the MCAT was very challenging for them, especially managing time during many weeks of straight "full-time" clinical rotations. At my school, RT classes weren't excruciatingly difficult, but they were definitely made to challenge us. Most of them also had to do 5 years to get their degree, not sure if this was due to scheduling issues, late decision to want to go MD, or both. But, those who are in or have completed med school all thought that the background as an RT was excellent clinical and patient experience and a great motivator for specialization (IM to fellowships in Crit Care or Pulm [RT background is excellent for Crit Care, btw], Anesthesiology, etc.).
On the other hand, becoming an RT is expensive and requires a lot of testing. We have a total of 3 exams... one is the entry-level CRT that costs about $200, and two parts (written and clinical situation simulation) for the advanced-level RRT that costs almost $350 I believe. Plus, in order to practice, you usually need to get your licensure which varies state-to-state (for me, it was another $100). $650 from my senior year of college to be able to work as an RRT. There are some discounts, but still expect a lot of moolah.
Basically, it won't hurt if you can still do your pre-req courses while doing the RT program. It is very, very doable! A bonus is that with BS programs you may become certified then registered and start working before you even get the actual degree which makes up for all that you spent to actually become an RT.