Making maraschino cherries is a bit involved... basically, you brine them and then flavor them. To keep them for a long time, you'll also need to can them.
Here's a great recipe for making the cherries, and here's instructions for canning.
The canning instructions are specifically for cherry topping, but you would use the same boiling-water canner process for maraschino cherries in their syrup.
To pit the cherries, I'd advise purchasing a cherry pitter (yes, there's actually a device for this) if you're going to be doing this very much.
tl;dr Either way is fine.
When making ice cream- your quest is to bind up water. Water crystallizes and makes ice cream icy instead of creamy. There are a lot of ways to keep water from freezing in ice cream from reducing the volume of water in the mix, to using natural antifreezes, to binding the water up with gums or starches.
Sugar loves water. The water will eagerly hook up with sugar and won't be able to freeze.
If you macerate your cherries two things will happen-
1- Water will be drawn out of the cherries and
2- The water that is left in them will be saturated with sugar and slower to freeze.
The result is that the cherries will be softer, sweeter (of course), be slightly more concentrated, and not freeze solid.
If you don't macerate them then they will be little chunks for cherry ice.
Both ways are perfectly tasty and I've had ice creams that do it either way. It just depends what you want to make.
Best Answer
I'm going to assume you're talking about the "whole fruit" style and not the "halved" style.
It depends on the producer and variety of cherry, but the cherries that I've seen are pitted in two different ways: in a similar way to olives and simply "brute force" pitted.
Like an olive:
The cherry is centered over a round(circular or elliptical) cutter and then a blade(you've seen the cute "X" shape at the bottom of an olive) pushes the cherry onto and the pit through the cutter.
Brute Force:
Since most cherry pits are "free"(they don't cling very hard to the pit) it is possible to simply center the cherry over a hole and press out the pit with a dowel or rod. The pit simply "squirts" out and the skin is split a little and the flesh on the opposite side is bruised a bit. This results in a cherry that looks more "whole" and retains more flesh and sometimes you can barely tell where the pit left the fruit.
However, like all industrial processes this can be done many different ways up to and including by hand depending on the producer and/or target cost/quality of the final product.