I would say the current answer is "It depends" based on that doc: :)
Are multi value extension attributes supported in Azure AD e.g. departmentnumber

Cowman. Alex (Enterprise Services)
0
Reputation points
We want to use a number of multi valued currently stored in on-premise AD user attributes and sync them using AD Connect for use with Azure based Applications e.g. departmentnumber & roomnumber multi value attributes.
It's not clear from the recent documentation I've read if this is supported or not i.e. I believe AD Connect will sync the data but I'm not sure if any azure based applications will be able to consume it.