Is it common for rental properties (e.g. bought with FHA loan that I'm still paying on, but I'm now renting and have rental insurance) to be considered "at risk"

Yes, you are 'at risk'. If you could lose your money and/or property that you put into your business or rental, you are considered 'at risk'. 

You are 'at risk' in any activity for:

1.   The money you contribute to the activity, and

2.   Amounts you borrow for use in the activity if:

• You are personally liable for repayment, or
• You pledge property (other than property used in the activity) as security for the loan.

Amounts not at risk include nonrecourse financing, or guarantees or agreements that limit the losses of the taxpayer.