As far as I know the road to Bowen Ranch is just fine for motorcycles, of course you have to get around mild ruts and washouts at times, and if you are skilled even minimally, you'll do OK. Mike Castro, the proprietor and gatekeeper at the ranch, has a particular dislike for dirt bikers who have no regard for rules or private property. If he doesn't chase you away with one of his armed tantrums let him know that you want to leave your bike at the parking area/campground and will abide by his rules, and the rules of the BLM and Forest Service.
I would also bring a knarly chain and strong lock to attach your vehicle to the stoutest tree you can find in the parking area, just to be safe. Some desert rats are, well, nasty creatures who need discouraging. The hot springs and creek environment is precious, so pack out everything you bring in plus other trash you find. Clothing Optional is the culture of the place and you should be comfortable with whatever you wear or don't wear, including nothing. Have a great visit and please post a report on your day's adventure, here on the Forum and also on the Facebook Group, "Deep Creek Hot Springs."
We all wish you the very best hot springs experience possible.