You may need a JS library to handle the compilation of LESS/SASS to CSS, but even then it's not absolutely mandatory. In theory a standard LESS/SASS pre-processed into CSS shouldn't require any accompanying JS files.
For example, in our Java applications we use a Maven plugin which handles the compilation: we tell it where the source files are, what the target directory is, and that's all there is.
SASS Maven plugin
SASS VS plugin
The nature of pre-processing is to handle everything at compile-time rather than run-time, so there shouldn't be a dependency on any JS frameworks.