Yes, the .svl file is a single layer from the session format, in XML. (The session format is itself an XML file, but compressed with bzip2 compression.)

One thing SV does lack is a layer file format that can easily be interchanged between SV itself (for label alignment) and a text editor (for bulk text changes). Neither is there any built-in text editor for editing the whole content of a text transcription at once. I suppose this has to do with the initial focus being on music rather than speech, and having no particular desire to "compete" with Praat.