I've done it.... When my oil cooler was leaking, it caused some oil to get in the coolant lines.

So I drained, replaced with water + simple green and ran the bleed procedure. It caused a lot of foaming. Drained again and kept running the bleed procedure with a garden hose in the coolant reservoir until all foaming stopped.

Drained and replaced with BMW blue.

Not sure if it was a good idea or not, but almost a year later and no issues.