Personally does not make any sense with single SSID ? if the both business units using different SSID, yes you can do multiple vlans or different department need to get different IP address only using different SSID, single SSID with 2 Differerent subnet (no control how the IP address allocated) - until you have any method to identify the end device.
Current customer wants to divide a /22 vlan into multiple /30 secondary vlans. - not sure /22 into /30 ? (that will be not a good ida) - not make any sense for me ?
No you should not do that! Your questions have already been answered on other posts. Please talk to a specialist designer to explain your requirements and let them propose a solution which meets those requirements. There is absolutely no need to split up a /22 subnet. There are various different ways that users can be put into different VLANs - but whichever solution you use it will usually involve radius and CoA.