Below mentioned are few points you should know prior going to NBU 7 dedupe option
1. NBU 7 deduplication option is nothing but a PureDisk integration into NBU
2. NBU deduplication option is very particular about hardware requirement. since you have not mentioned Red Hat OS version, check the NBU 7 compatibility list
3. Deduplication cannot be enabled if you have 32 Bit hardware & OS
4. You have mentioned that you are going to upgrade your existing NBU 6.5.4 to NBU 7. Make sure that your master server is 64 Bit hardware and OS otherwise deduplication will not work
5. Symantec recommends not enabling deduplication on master server as deduplication loads the CPU and if your existing server is having load then you end up in performance issue. But if your master server hardware is capable of taking the load the deduplication then you can enable the same on master server itself.
FYI - I have enabled deduplication on master and it is working fine.
Suggestion - You have mentioned that you are going to replication backup data to DR site. Then why not replicating NBU catalog to DR NBU server. NBU 7 RealTime can help you with this.
Hope this answers your queries.