The answer is, we don't know and how much risk will you take.
I asked this of the OCC and they said HUD has to make the call. I'm waiting.... I haven't heard of anyone getting into trouble on it, but here are some points I asked and my thoughts.
Is the link a thing of value? Likely yes. Could be a problem
but many regulators (not rule makers) seem to think this will not be a huge issue in practical application.
The letter of the law may differ, however.
What if there is a reciprocal link between each site, is it a marketing exception? Could be.
What if one site has 100M hits per month and the other has 100? Maybe the marketing exception isn't so reciprocal.