Hi Martin,
Yes of course! Inter-BSSID (APs with the same SSID) roaming is part of the Wi-Fi standard, so in theory, you can setup access points from different vendors with the same configuration and a Wi-Fi client will roam accross them. In reality you'd probably find the roaming wouldn't be particularly seamless, but it would work.
The 4 x Ruckus APs you have will be operating independently of each other but providing you configure them with the same WLAN details, then your clients will connect and roam between them on a single SSID.
Should you have any roaming issues then I'd recommend keeping your eye on eBay or similar to see if you can find a ZoneDirector 1100/1200 as this will then provide you with centralised management and monitoring and improve roaming and client management.
Hope that helps,
Darrel.