I'm not sure if your friend is ethically justified in joining a group and changing its culture to suit their taste. Why should their subjective sensibilities take priority over those of the majority where there are conflicts? Yes, some compromise is to be expected with certain norms, but swear words are, frankly, most likely harmless to the people in this group and your friend risks intruding. It is impossible to accommodate for every person's desires perfectly, and attempting to do so will only lead to a bland, artificial society.

But there is also a business case for this. If the group works well and cohesively and swearing is indeed part of the culture, then imposing such rules can be extremely harmful for morale. There is no guarantee that banning swearing will improve the environment for anyone but the new person, and that's bad for everybody.

Edit: to clarify, the line is obviously subjective, because ultimately it depends on the tastes of everyone involved. Because undirected swearing in a stressful adult environment is largely harmless, it should not be subject restriction based on moral grounds. Otherwise you're imposing culture based on what individuals find unpleasant, which is a recipe for a very oppressive structure.

There's no guaranteed harm in bringing it up and politely asking once, but sometimes participation in an existing group requires some degree of conformity, or at least tolerance. Some people may judge a newcomer who asks, it may be better to wait until one has established a positive reputation.