Well, this should teach me to take a little more time researching articles.
There's yet another way for account managers to extract money. Some of them charge a fee "per lot traded" in your account. This means that churning accounts isn't just limited to account managers with an IB relationship.
A friend also pointed out to me that there may be more exemptions to NFA registration requirements for account managers in the spot forex market than I thought. I looked again. The regs clearly state that forex account managers must be registered with the NFA, then list a pile of exemptions. Personally, I'd feel safer with a registered account manager if the company is in the US.
My friend had a second suggestion. Some forex account managers or account management companies are independently audited. This is definitely a good thing. Just check to make sure the auditing company is truly an independent auditor and not really a company either working for the account manager or a company that's getting a commission for referring new clients for forex managed accounts.