At the risk of sounding pedantic, it depends on what your objective is.
If you’re trying to do network based load sharing as a “single” IP address they need to be on the same VLAN, and you need to look up the Microsoft Knowledge-Base articles on load balancing.
If you want them to appear as a resource to multiple VLANs, then, by all means put them on separate VLANs.
If you want to use the second adapter as a private channel to a database server (I’ve seen multiple instances of this), then the VLAN question drops out, since a “back channel” is usually a direct, crossover connection (or through a small switch) between the front-end server, and the back-end server. I’m sure other folks will chime in with possibilities I’v not mentioned.
The key point in all of this is – Bear in mind exactly what you’re trying to accomplish! I’ve also seen servers with multiple LAN connections, and all but one sat idle!.