No limitations have been mentioned for hybrids. There are some cannon cases of hybrids having offspring:
In The Drumhead, crewman Simon Tarses is put on trial and suspected of having falsified his origins as 1/4 Vulcan, when he is in fact 1/4 Romulan (to which he pleads the fifth seventh).
Crewman Daniels was also of multiple origins, one of which was Vulcan, suggesting that interbreeding is quite extended by the 31st century.