But frankly Omnivista will be the One NMW that supports Alcatel Switches best.
As Extreme Management Center will work best with Extreme/Enterasys, as Cisco Prime/One/... will work best with Cisco gear.
If you have only Alcatel: i would use Omnivista. If you have different Verndors and only want to monitor Chosose Nagios/PRTG/Solwarwinds whatever.
If you want to do Management (Firmware upgrade/Config changes/...) i guess multivendor will be hard once you are out of the "enable or disable a port" zone.