Doing wet lab research is highly encouraged at certain IM fellowships (esp oncology, allergy, rheum) at the more prestigious institutions, as well as in the middle of general surgery residencies. During this time you are typically funded under by your department (generally a T32) Based on your track record during fellowship (publications), you can apply for the K award series of grants which is restricted to those with MD or MD/PhD, which is a sort of mentored-training grant as a bridge to independent funding (i.e. the R01). Usually the difficult part is transitioning from the junior faculty, K-awardee into the R01, for which the payline has been hovering around 10-12% of submissions awarded, which is extremely competitive. Keep in mind you are now competing against those who perform lab research full time (the PhDs), and so will take a huge cut in your clinical work and your salary to make it. At this point, many choose to either enter industry, or transition to a clinical role. From the faculty I have spoken to about this, many of whom are MD only, the first step is to find an excellent residency, ideally something non-procedural (IM, Peds).
Look at the faculty at top 20 IM departments, many of them are doing incredible basic research with only an MD. The PhD is mostly helpful because you don't have to worry about loans when you are making less money as a researcher. By the time the MD/PhD gets back into the lab, 6 years after defending their thesis (2 years clinical rotations+3 years IM residency or more + 1-2 years clinical fellowship), the lab stuff has passed them by and your skills are not that dissimilar.