Answer says TLD files may be place in "any" sub-dir of WEB-INF. "Any sub-dir" could refer to lib or classes as well and it should be place in WEB-INF or a sub-dir for TLDs.
I remeber from the spec that the TLD files msy be placed in "any" sub-directory but should not be placed in classes and lib directories. So there is "should not" not "must not". So this may be valid but these directories are made for diff. purpose.