Yes, lots of small companies use Starline brass, heck even some sizeable companies. Especially since the obama shortages, and then covid, the major manufactures shifted to all their in house production (Winchester, Lapua, Norma, Petersen, Hornady for example), Remington was stopped during their bankruptcy, and is going again, but most of their new brass is going to ammo production too, both Rem branded and other Vista brands. That left Armscor, Starline, and Jagemann. Ammo Inc bought Jagemann and it seems to be mostly going to there internal production now. There are a few other small brass makers (Quality Cartridges for ex.), but nothing in the numbers of Armscor and Starline. Hornady, brass is starting to show up again in decent numbers. Variety of brass, the nod goes to Starline and Hornady.
Starline is basically the go to brass company for all small manufacturers, with a few high end exceptions.
Pro Tip: If you're loading with new brass......it's not reloading by definition.