I'm no expert, but from what little experience I do have...the normal "hitch hikers" won't hurt the plants...if they aren't overtaking yer tank I don't see what harm they can do (but that may be a newbie assumption)...
I had one show up when I added plants to my 12g fluval and he is still just chillin in the tank, he will eat algae but not really enough to make a difference...
Though keep an eye on how much you are feeding yer fish because from my research (I was in the same boat as you sorta, I saw a snail that I didn't buy and was like wtf) I gave learned that if you over feed you will for sure have a ton of snails...
If they are a decent size, take a pic and someone can prolly ID them and let you know if they are harmful or not tho...but yeah...watch how much you feed...