Using struts tag libraries with *any* Spring-backed project isn't a Spring Social question...it's more a question of what parts of Spring are you using and what parts of Struts are you using?
I assume that what you're really asking is if you can use Spring Social's ConnectController and/or ProviderSignInController alongside an application full of Struts actions and yet still be able to use Struts JSP tags on the views that Spring Social presents. You should be able to, I'd think, but I've not really done any Struts work in years, so I can't say what's involved...other than to offer that you could configure the controllers' views to redirect to a Struts action-backed URL and then it most certainly would work.
That said, you might benefit from developing a Struts equivalent of ConnectController/ProviderSignInController. Again, I've not explored what would be involved in using Spring Social in Struts, but I see no reason that it couldn't work, if you're willing to put a bit of effort into learning how Spring Social works and recreating the controller bits into actions.
Spring Social Project Lead