The local Latin Mass community does it all the time. Usually Marian or Eucharistic, for the entrance, offertory, and recessional. (Usually by the girls' choir rather than the schola, though.)
From my understanding of the old rubrics, vernacular hymns may be sung at low mass in place of the introit, offertory and communion as well as during the exit procession at the end of mass. However, the ordinary is not to be sung.
It may be worth nothing at Summorum Pontificum also permits the readings to be proclaimed in the vernacular without having to be read in latin at low mass. However, they must be done in Latin at high mass.
The way I have read the documents and practiced it was that during High Mass, Latin only between the Introit and the Communion chants, and English is permissable on either side of that.
To participate in the discussions on Catholic church music, sign in or register as a forum member, The forum is a project of the Church Music Association of America.