Package uploads by non-maintainers are allowed (there may be license issues, but most packages if not all on hackage have licenses permitting this), but of course they are not usually done. They are tolerated if done in good faith and with reasonable procedure. If you contact the maintainer and don't get any response within n weeks (where I'm not sure what the appropriate value of n is, not less than 3, I'd say), uploading a new version yourself becomes an option, discussing that on the mailing lists seems however more prudent. If the package looks like it is abandoned, even taking over maintainership - of course after again contacting the maintainer, giving her/him time to respond - may be the appropriate action, but that should definitely be discussed with the community (haskell-cafe or mailing list, for example). Whether to prefer a non-maintainer upload or a fork must be left to your judgment, personally I tend to believe forks step on fewer people's toes.
But a better founded reply would be possible if we knew which package is concerned and could look at the concrete situation.