Check the park website (nps.gov/yell) for information about which lodgings/restaurants will be open inside the park. Probably not much - by November, when the snow usually starts falling in earnest, they will stop keeping the roads clear and letting the snow build up in preparation for the winter season.
Grizzly RV's closing date this fall is October 15th, by the way. Other CGs will have already closed, but there may be some open.
That said, you're more likely to be able to access the park in late October than you would be in April, since roads are not likely to be snow-packed yet.
