It's fine to just cut them out, making sure not to cut the skin while you do it. Long-haired pig do tend to get mats, particularly around their hind end. Regularly trimming their bum area to keep the hair there shorter can help prevent mats in the future and keep them from getting pee on their fur.
Brushing can help, and if you have a piggie that likes brushing that's enormously helpful! My long-haired pig hates brushing/clipping and it's difficult to keep on top of her coat... we end up with one person holding all four feet off the ground so she can't run off and I just grab long pieces in the back and cut the shorter, so she always has a really weird haircut going on! LOL!