I do not do this type of printing, but I do believe that if your printer has solvent inks, it should be fine to print vinyl with, however if they are pigment I think they would need to be sealed. If you look in this section
Vinyl Signs and Decals - T-Shirt Forums, you should be able to find more information on what types of inks do not need a sealant.
Also using the search feature at the top of the page may bring you some results as well.