Dear Wale idowu,
If your redundant Unit is in a different subnet and different VLAN then Just make sure that your redundant Unit is able to talk to primary Unit and AP's & vice versa. Also refer to ZD user guide to ensure that all ports for ZD to ZD comms & AP's are opened both ways. Also make use of limited ZD discovery feature on the ZD so that both ZD's IP even if in different subnet and VLAN are learnt by AP's.
Also test it out sufficiently so that any glitches in such configuration are addressed.
As far as i know, Management IP is used for managing the whichever active or primary ZD for monitoring by admin and does not play any role in redundancy.
Redundant Unit must have unique ipv4 config IP address preferably same subnet as primary Unit.
peer IP address is unique ipv4 config IP address preferably same subnet as primary Unit and has to be configured manually in Redundant Unit first, then put to network then configured from primary Unit. Refer to ZD user guide for the step by step process.
Idealy both ZD should have same license count however in your case your no of AP's are less that your ZD AP license so that should not be a issue.
zd user guide is available here -->
https://support.ruckuswireless.com/do...
Hope this helps