Of course you can start a new data zone/ a new NetWorker server.
By default, a NW eval license will be valid for 90 days.
Because of a new licensing scheme you need a new (NW 9 license) anyway.
You must not necessarily remove the old license from the current server. So there is no licensing issue.
You have 2 licensed data zones but Dell/EMC just counts the backup volume capacity. So this should not be an issue.
I'm running two implementations of Networker Server 184.108.40.206 on AIX, and Networker Server 220.127.116.11 on SUSE. So long as the old implementation is only being used for restores, it simply doesn't need licencing.
In the event of a disaster, EMC lets you bootstrap recover your backup server, and begin restores before you need licencing from EMC for the new hardware. The tricky part is the transition period, however when I was switching environments I discovered as mentioned above that new implementations come with a 90 day eval license, so you do have 90 days to make your gradual migration.
Now, the reason I'm still running 18.104.22.168 for restores is because you SHOULD be able to scan existing volumes and index them and have it pull the correct expire times from the metadata, however I tried twice and that was not the case, it was giving scanned savesets and expire date 30 days from the date I scanned the volume. This behavior is incorrect but 6 months of a support case couldn't figure out why it was happening. This may have been fixed since I last tried it, which would have been about a year ago on 22.214.171.124.