Heartwood being more brittle, I ensure that it is oiled more before knocking in and during knocking in. My observation has been it is worthwhile to give it an additional coat of oil. In the past I have observed small edge cracks appear on the heartwood side of the bat during the knocking in process because of the brittle nature, but my recent bat has about half an inch of heartwood and an extra coat of oil has ensured that this doesn't happen. Also, I was gentle with the knocking in, before gradually increasing the intensity on the edge.
While I cannot attribute the lack of any edge cracks to the extra coat of oil OR the gradual knocking in, but can vouch that both when combined worked for me. Moreover, I like that look of a cricket bat with a little bit of heartwood and while I am told that it performs better, I haven't found any conclusive evidence to the same. I go for it purely because of looks.
One more thing, add an extra layer of fibre glass edge tape on the edge with heartwood on it. Serves as an extra layer really.
Cheers