While businesses can't sign up directly, most of the US-based programs have a second, parallel program for businesses, separate from the individual FF accounts.

For example, right now at United it's PerksPlus. It's a revenue based program with a multiplier for class of service. So, for example, if your company spends a total of $40k on heavily discounted coach tickets, the company earns a free round trip domestic ticket, in addition to whatever the individual flyers earn in their accounts.