Under the Single Domain License - is it ok to offer the embed code for the licensed player to other sites in order to promote media hosted in the licensed domain? Are the "Embed" and "Viral" plugins legal to use in order to let other sites feature my videos if I buy a Single Domain License?

GA - yes, it's okay to offer the embed code w/ a single domain license, no problem. And yes, it's legal to use the Embed and Viral plugins as well.