There is a couple of thing you can look for.
If you press the pineapple lightly with your finger it should have a little give to it. You can also tap the pineapple with the palm of your hand the sound that it makes should be muffled, not hollow sounding.
Avoid pineapples with spots or...
I have never tried to pork on a salad. I use a marinade for pork that uses apple-cider vingar, diced apples, dried cranberries, and EVOO. It may work for a dressing.
A tip I picked up a few years ago is to sear the meat before you start it on the rotisserie. This help lock the juices in to the meat in the beginning stages so you dont end up with a dry product.
Brushing the pineapple with a oil or a glaze is not necessary. But depending on the dish you are making a glaze can enchance the flavor. Personal when I grill pineapples I dont brush with anything I do however dizzle them with a little honey butter right when they come off the grill.