There are many species of ornamental grasses. You have to identify what grasses you are referring to. Many ornamental grasses are propagated by division and some by seed. Many grass cultivars do not come true from seed, so a particular seedling may or may not be identical to its parent.
Some grasses may be invasive and not recommended to propagate by seed.
A good book to reference in the library is The Encyclopedia of Ornamental Grasses by John Greenlee.