Never know if you don't ask. I know our group welcomes others as long as they have a helmet on. Its a rule for insurance reasons. We used to have a larger group it split when the helmet rule went into effect. One guy made a huge stink and he took half the group. You will know within a few miles if you can keep up or not, or if you peel off letting them go on ahead.
I know I have made more good friends bike riding, went camping this weekend with them. Lots of fun. Ask, all they can say is no.