It appears to have installed into lib/perl5/Probe/Perl.pm (in a directory on the PERL5LIB path), but it seems that nothing in that directory can be USEd.

If the file is located at /foo/lib/perl5/Probe/Perl.pm, You need to add /foo/lib/perl5 to PERL5LIB. Adding /foo is useless as far as finding this module is concerned.