The answer is yes, there are some areas to temporarily park your RV in Yellowstone, and longer-term at some of the lodging parking lots.  However, there are not as many designated pull-offs as some other parks you may have been to...  Also, RVs longer than 25 feet are also restricted on some secondary roads in the park. 

You can drive the main roads in Yellowstone, and you can enter the Park at any of the five entrances - though the easiest entrances to Yellowstone for RV navigation (i.e. less tricky driving) are via West Yellowstone, Jackson Hole, Gardiner and Cody...  There is a great RV campground at Fishing Bridge, on the north end of Yellowstone Lake.

Again, there will be a few areas where large vehicles are prohibited, and most of the camping areas don't provide hookups.  Flagg Ranch, Colter Bay and Fishing Bridge are the few locations that do.

Thanks for the question.  Make sure to report back on your experience at OhRanger.com and let others know of great RV destinations, pull-offs and other ideas in the park!