A PD is not gonna care that you did a rheumatology elective in July unless you fail it. If you can get a solid LOR from it, great. But a LOR from your sub-i at a university will matter much more.
Since you are a DO, I actually understand your reasoning behind doing 2 sub-I's. Schedule those sub-I's early (July-Sept). Schedule the 1st sub-i at a community ACGME program, get your **** together, and schedule another sub-i at an university program that will let you rotate there. Apply to a ton of places on VSAS because some of these programs take awhile to respond and/or have limited spots for outside students. It is actually easier to get subspecialty rotations at universities vs. IM sub-I's because of the limited availability of spots. If you really feel like you're a boss, do an ICU away rotation.
I would only advise this for DO students who actually have stellar board scores (COMLEX & USMLE), because these audition rotations aren't gonna get you interviews when you have ****ty board scores (well, maybe a courtesy interview... but not a high spot on their rank list).