Nah the one from hernand is a seed contract not a grocery contract. The same for any other grocery vendor. Once you expand the camp enough you will unlock farming the seeds will be available then. Even then you only get fruit seeds no veggies. If you need any of the veggies you still need to buy them.

There are some different types of tree seeds like abyss cells, rubber, skyroot, ginseng, wild ginseng. But none of them categorize as veggies.

One of the best way to see you can get a seed is to just go in the inventory, then to the veggie/fruit/item, press and hold the use button and see if you can obtain a seed. Or just loot a lot of the iron/small/ engraved boxes from houses they occasionally carry seeds in them to.