User invite to team

If adding a user to a team, do I need to ask them to check there email and accept the invitation?

If you call teams.createMembership(), client side, yes

Is there a way to add a user to a team without having them go through the invite and accept invitation process?

For example, the app I am looking to create is going to be a meetup style app where users can be members of multiple community groups via a group code, so when they join a group, I would want to add them to the team automatically so that the permissions on documents related to a specific team are already in palce