I don't think the tenders are a problem, unless the seas are very rough. I noticed on my last Princess cruise (and on HAL) they have a special procedure for getting folks in wheelchairs on the tenders. After all the able-bodied passengers are on, they slide a board across from the deck to the tender, and wheel the passengers right onboard. The wheelchair pax are then secured right in that entryway area, the board is rolled away, and off the tender goes.
I think the only time they will request that wheelchair pax not tender into port is if the seas are so rough as to make using the board too dangerous.
Of course, I'm just describing this procedure from a layman's point of view. I am sure someone else can offer more insight into how they do it.
Blue skies ...
--rita