Answer: The seed viability would depend on several factors including maturity before frost, and the variety of grass in question. Some of the ornamental grasses do set viable seed which comes true while others do not. Your success in starting the seeds would further depend on the quality of the seed and on your seed storage and on your seed starting and raising techniques. So in my opinion the salesperson was hedging in a reasonable direction in the sense that seed based production of ornamental grasses is somewhat unreliable -- so much so in fact that commercial propagation is done by root divisions. On the other hand, it's always fun to experiment!
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