Is it possible to update ADMN (that is working in separate intranet) without access to Internet?
no it is not possible.
the virus update definitions that are available to download separately cant be used for ADNM
you could put an AMS in a perimiter network and have a second AMS download from the AMS that resides in the perimiter network and how your clients update from the second level AMS. That way your clients are not directly connected to the internet or perimiter network and remain secure.
make sure the AMS servers are multihomed so you can also physically as logicly seperate the networks and firewall the cards seperately.