Doubt anyone here would argue with Harry Soo, and he's right. Applewood is great.
If you want to use hickory though, go ahead. I just wouldn't use too much, and by all means, don't add any more midcook.
Personally, I like fruitwoods for ribs and poultry but the smoke often peters out sooner than I'd like. Lots of folks simply add more, but I don't like to add wood midcook since the initial smoke can be pretty nasty when the chunks first start smoking.
My favorite nowadays for ribs and poultry is probably pecan. Being a good dense nutwood and in the hickory family, it smokes for a good long time, but after seasoning it's quite a bit milder than the other hickories and oak. Not everyone can go to the store and pick up pecan, though, so lots of folks compromise and use a combo of fruitwood and hickory or oak. For example, two medium chunks of apple to one of hickory is a popular choice for ribs in a wsm.
By the way, if you use water in the pan or foil the ribs fairly early, you can get away with more smoke, but bottom line is that most folks probably oversmoke ribs. Just my opinion, of course.