Google made sure that Google+ Pages could not be used for spamming by blocking them from interacting with profiles which are not following them.

But this seems to have changed as Google+ Pages are now able to post comments or +1 posts made by such profiles.

Google+ Help pages are not updated to mention this change. It still states:

If you’re worried about how deeply a page can interact with your Google+ profile, don’t be. Unless you show that you’re interested in a page by adding it to a circle or mentioning it, there’s very little that page can do to reach out to you.