If the credits only benefit the borrower and do not offset some other cost for the other participants in the credit arrangement then I think it would probably be ok. You are right that the arrangement would constitute a referral but you need to establish that a thing of value is going to the person doing the referral for there to be an issue. For example, if you started paying the credit on behalf of the realtor or reimbursing the other parties then you are providing a thing of value to someone who is referring to you.
Outside of Section 8 though, you need to make sure the terms of this credit are explained and the credit actually happens.
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Opinions expressed are my own and do not reflect legal advice or the opinions of my employer.