Polyp's cropping up.....friends or foes?

[newreefer_59]

My 150 gallon tank has been up for a year now, and in the past few months i have had several (about a dozen actually) of these polyp's appear on some live rock. The coral I presently have are:

Monti
Bird's Nest
Hydnophora-Horn Coral
Digitata
Zoanthid Button Polyp
Pink Button Polyp - Zoa
Red Open Brain
Acan Lord
Australian Acan
Clove Polyp
Chalice

Can these polyps potentialy harm these or any coral and should they be removed?

Many thanks.