Hi Friend,
In general, roaming means, when a client move from one AP to another AP on the same SSID means, associating SSID should be same . when SSIDs are different the association process should start from the beginning ( re connection ).
the benefit of the roaming process is , it will avoid reconnection ( possible to avoid re authentication with OKC).
When both SSIDs are mapped to the same VLAN then it is called L2 roaming other wise is both are mapped to two different VLANs it is called L3 roaming.
Aruba can easily handle L3 roaming with in the same controller but you have configure IP mobility in case both SSIDs ( VAPs ) belongs to two different Controllers.
In your case I understood that, you are trying to deploy WLAN with two different SSIDs and VLANs, there is no way handle roaming in such scenario, client has to be deauthnticated from the first association (SSID) and it has to initiate association process with the new SSID.
As Victor suggested, you have to configure same VAP with VLAN pool or two different AP groups, different VAPs with different VLANs but SSID should be same.
Hope you got some more clarity.
Please feel free for any further query on this.