I think the most damning part of Rowena's modus operandi is more related to her payment options. To wit, she does not pay out a single gil, instead giving scrip to her workers (though I might be misremembering). Scrip good for exchange only at Rowena's businesses, for Rowena's goods, while they are already indebted to her for their training, room and food.
That's basically a company town system, if I remember well, and it's pretty characteristic exploitation. It perhaps isn't the unkindest, but those under Rowena's employ do not really have much in other options beyond continuing with Rowena, or striking out to form their own business and sell to her (which, harpy that she claims to be, she still takes in trade well and offers partners to Zhloe, and Sanana (sic) with Kurenai does have her own solid business now, even if it probably links to the EATC or House of Splendors too). Also, the debts do stack up fast, and for people and countries that had company towns, it meant very little of the wealth stayed with the local people and they had very precarious conditions (since the employer, who paid them and housed them, was the one who chose basically what goods to bring in for their good and use as well).
That said, beyond Rowena being unforgiving with and having a high interest for debts she is owed, she does not seem to have her Splendors employees in such drastically bad conditions as some of the infamous company towns. Overworked, yes, and they grouse about that. So Lady Eboshi is probably a good close comparison.
I'm assuming that for the Domans, who are getting back on their feet, it is probably close to a deal with a very exacting devil that will have sharp interest rates, and is very capable of screwing them over. And for us adventurers, well, we are both Rowena's providers of some of the bizarre goods and her clientele. We're freer from her grasp because we buy so many of their goods, and because later she can absolutely use that as marketing (the Warrior of Light trusts her wares!) on top of being able to provide goods and services she needs back.
I mean we -are- cleaning up an island of nasties so she and the EATC can have a less heavily taxed port of call in the East, and anything there is provided out of their pockets. We're a good investment.