I'm not sure about bought seed, but violets fling their seeds into all manner of inhospitable places and sprout.

For me, they have great success in the fine grit I use on my bonsai...Not much shows on top, but the root structure is awesome! Once it has its paws under the table, then it starts leafing up and flowering.

The seeds seem to do best in little crevices where moisture gathers and drains, the ground is coolish, and there is a dusting of leaf mold. Good light, but not all day. The ones with more shelter seem to bulk up better.

I suspect thin sowing would be better. The seedlings are mostly solitary, probably because of their distribution system. (and with root systems like theirs, who needs competition?!)

I'm not sure about the cool treatment: they seem to start into growth in the autumn - a couple of little leaves or so, and spend winter colonising with their roots. If you have a cool glasshouse that gets no more than 5 degrees of frost they won't mind. (The v. odorata, at any rate.)

It is recommended that seed be sown in late winter or early spring, I know: I'm only reporting what I've seen in my own garden.