When we have valet parked, we've almost always been offerd help to get DD's wheelchair in and out of the back of our van (even though we can easily handle it). The CMs actually usually look disappointed if we refuse.
So, I'd expect that most of the time, it won't be a problem. They may be busy, as ducklite mentioned, but if you smile and let them know you need help, it should work out most of the time.