Yes, you're correct about the VS add-in only supporting web apps at the moment. So you're looking to use it to publish SSDT database projects too?
This is something that is on our backlog, actually quite soon. We'll also be extending the RgPublish command line with the same functionality.
There are workarounds available (for command line based publishing only) that I can provide if you're not able to wait for this.
Redgate Software Ltd