Do I need to maintain ReSharper's dotsettings.user file in Source Control?

No, the dotSettings.user file should be excluded from source control. It has user specific information in it, and shouldn't be shared, e.g. bookmarks, unit test session windows.

The .dotSettings contains project or solution specific settings that can be shared with the team, e.g. naming standards or braces layout. If you wish to share these amongst teams then the file should be included.

No, you shouldn't do so, as ReSharper Help says.

The corresponding settings file .sln.DotSettings is saved in the solution folder.

As soon as this file is added to your VCS and the team members get it, they will have settings from this file applied automatically without reloading the solution.1

The corresponding settings file .sln.DotSettings.user is saved in the solution folder. You should not add it to your VCS.2

The article explains ReSharper setting layers in details, which answers your questions as well.