Let’s say I hypothetically got a check from my HRA company, but which I, being a baboon, did not read as closely as I should, and did not notice that it was intended for a bill my network did not cover and assumed the check was a payback from an overpayment prior to the new ARRA kicking in (as I said, I did not read too closely and am a baboon). I then used the check to pay for my next two insurance payments. Can I get in trouble for this, and should I tell them? Or should I just pay for what the check was intended and leave them out of it? 
I have no idea what HRA and ARRA stand for, but my guess is that the HRA check was made out in your name. So the intention was that you can put it in your bank, and then you’ll have enough money for the other stuff. So now go pay for that other stuff, and all will be as it should be.
Just pay your out of network bill and don’t worry about it.
Remember, the R in HRA stands for reimbursement. In most cases, you have a bill you already paid that you have submitted for reimbursement. You are free to do whatever you want with the cash you get back because the bill has already been paid (at least from the provider’s point of view in the case of payment by credit card). At my company we usually ask for evidence that payment has already been made, although we’ve been known to accept a bill as documentation. We actually had one woman submit a bill that showed the cost of the service, expected insurance coverage, and the balance that the employee was responsible for. We paid this amount, then found out that the insurance had paid more than expected (or the dentist, I think it was, had made an adjustment downward, I forget which) and the employee had been over-reimbursed. We did make sure we got the money back.