Lilypond originally was developed using LaTeX, but the current version does not use TeX at all to produce its output of graphical music scores. So questions about Lilypond's syntax (or the Scheme syntax used to modify it) are off topic.
As with any program that produces graphical output (Inkscape, Gimp, Photoshop), you can include the output graphic files into a LaTeX document using
\includegraphics from the
graphicx package. From the TeX engine's perspective these files are just big boxes to put on the page; it doesn't matter whether it's music or pictures inside. Questions about doing this are only on topic if they relate to how TeX gets and arranges that box on the page.
The Lilypond documentation gives the impression that the program is closely integrated with LaTeX because there is a
lilypond-book program that includes Lilypond images within a LaTeX file. This program is basically just an automated way of processing each separate image with Lilypond and then using
\includegraphics. (In fact in many cases it is, in my opinion, simpler just to do it that way manually.)
As an active Lilypond user, I would encourage users to please start posting and answering Lilypond questions on StackOverflow with the
lilypond tag. The lilypond-user mailing list is currently the main place where lilypond questions are discussed, but the Q/A format and resulting knowledge base of SO would in my opinion be more helpful to the Lilypond community in the long run.