Is it possible to create a multipath iSCSI target with two DRBD nodes?

Ok that was easy enough to make me feel stupid for not finding it with google in the first place.

Short answer: no

Better answer: as people from the iSCSI Enterprise Target mailing list told me, this has been already discussed in the past and is not possible with current implementations, because the two iSCSI targets would need to have some shared state and talk to each other. This feature per se has not been implemented in any linux iSCSI target, and most probably it won't ever. This is because the main (only?) useful use case is in conjunction with DRBD and if its data path between the two nodes gets interrupted we would need really fast and really hard fencing of one node (details in the linked blog entry).