You can have both installed at the same time, and each will do its own thing. The shame is that Postmatic Social Commenting has no plans to do site signup, and Social Login Plugin won’t authenticate comments. They are two separate environments and each sees the world very differently. How do I know? I asked them both the same question.
Are you using AskBug? if so, update is available for download.
A fix has been pushed to tags and AnsPress