Yes, I haven't been on a cruise yet that didn't have people onboard who relied on wheelchairs. Most ships also have cabins that are specially designated for wheelchair users an are suppossed to be easier to manoevre around in than the standard cabins. I've never been in one, so am not speaking from personal experience. I think cruise ships are great for catering for various types of disability (i'm badly visually impaired) and find them much easier than hotels to get around. One word of caution is that some ports of call involve tendering to get to shore (being transferred to a smaller launch boat (usually ship's lifebaots) to get ashore) because the port is too small and the ship too big. these are not impossible for wheelchair users but are definitely more difficult, especially if the sea is choppy. So it might be best to avoid a cruise that has tendering at a lot of the prots of call.
Would add not all ports are wheel-chair friendly and not all tours are but it is a good holiday for all abilities,but check with cruise line what they can supply in way of hoists if needed,RCI seem to offer a good service from Southampton worth a look try out side school holidays.good luck?