Full explanation: Differences in DRBD resources - #6 by ghernadi
In short, you’re fine.
If Linstor has created a “tie breaker” resource by itself then it can remove it when no longer required. But if Cloudstack has created a “diskless” resource somewhere, Linstor will never delete it by itself.
An even number of participants is not a problem either. With 4 participants the quorum is 3, the same as if there were 5 participants. This means with 4 participants it can only withstand loss of one member, but that’s the same as with 3 participants.