I know this isn't ideal but in our current Git beta there is a feature called "Working folder" which allows you to link Source Control for Oracle to an artbitrary directory on disk which itself can be under source control via Mercurial.
It is perhaps worth trying out.
(The work that I've done adding Git support should make Mercurial support easier in the future)
It is essential for us too
Larry Talley commented
I vote with Brian for Mercurial support for Oracle version control!
Brian Lieb commented
I have used Redgate tools for quite awhile. Recently I have moved to a job where there is no source control of our Database objects in the oracle database.
The organization recently moved to Mercurial, and is not likely to add a new repo software, so if Hg was to be supported I am sure that we would purchase this product immediately.