||After discussing this question with the client the decision is that using OSM data for the test set is NOT allowed (neither for training, nor for inference). Of course you can still use OSM for the training tiles. I am sorry for this late announcement and the confusion this has caused.
As some of you correctly pointed out, this is in contrast to the previous Spacenet contest where OSM data could (and was) used during inference. The reason for this difference is that OSM building footprints in the test regions were not available in such high quality as road networks, so using them had much smaller effect than in the current contest.