Absolutely, ants can serve as pollinators. Some plants have even evolved to take specific advantage of ants. Those with flowers that exude lots of nectar to the outside are prime candidates.

If you want lots of butterflies, you need to provide the right kinds of flowers for them, too.

Ants visit flowers in search of food of some kind. Maybe other insects, maybe nectar, maybe moisture. Sometimes, they can cause damage by biting into hidden nectaries (which of course is not good for the plant).