The u3a theme, u3a plugins and selected third party plugins are supplied on installation and supported by the SiteWorks team.
u3as can install other plugins at their own risk but some may conflict with SiteWorks plugins. u3as raising support issues may be asked to disable additional plugins and confirm their issue is still present. If you do install 3rd party plugins then do due diligence – how many installations are there, what is user feedback like and how often is it updated and maintained? Ask on the u3a WP forum. Also try the plugin out on Local WP first and not your live site.
Moving forward, it is possible that the SiteWorks team will test the compatibility of plugins to meet functionality requested by the u3a community. This could lead to a list of plugins that would be supported to some degree on a best endeavours basis.
Also see below Can I use the SiteWorks theme and plugins on our existing WordPress website? and Can the SiteWorks team help if our WordPress site is hosted on our own site?