Yes, you can get 4* units from seed (free) gacha. The only ones I've yet to get are Hibiscus and Snowflake.
As for Lilac (new 4*), no idea if she's already in the seed gacha. If she's not, she'll be added once that limited gacha thing for her is over (probably?).
And yes, I had the same issue in getting pierce units. I already have Cary Ophyllus and Marigold evolved when I pulled Canola from the seed gacha.