This really depends on what fault features and functionalities you are looking for. When talking about multiple VLANs, one of the things you might be looking for is the ability to partition the views in the NOC by VLAN. This is commonly called a customer network managed view. There's a white paper on it located at:
http://www.cisco.com/en/US/products/sw/netmgtsw/ps996/products_white_paper09186a0080091c28.shtml
There are a number of other variables that you need to consider. For example, what other network modules need to be monitored? Are there servers and applications, also web-based applications that are considered mission critical? Do these pieces need to be proactively monitored or can they be passively monitored? There are many options wrt fault and performance management. I recommend you determine what you expect from a fault management system, then evaluate the different network management products to make the best decision. That said, I would like to add from personal experience that you can leverage a lot with a Cisco environment and a Cisco network management system such as Cisco Works, NNM, or Cisco Info Center. Don't only look at the ability to collect fault/performance events, but also what tools are included to help troubleshoot and debug to reduce the Mean Time To Resolution (MTTR) of an event and an automated wayof determining how a fault impacts your network services and customers.
