But HTML::Validator actually uses nsgml. SGML library contains DTDs, you need them in any case, you can install it in any location, so it shouldn't be a problem.

Update: note, that sgml-library is not something you should compile and execute, it just text (SGML, XML, DTD) documents.

Update2: there are also other modules that may be interesting for you: HTML::Lint and HTML::Tidy. Tidy requires libtidy, so maybe this is not your choice, and Lint is a pure perl module.