Microsoft's Storage Server NAS product can be successfully booted from a SAN -- or at least some SANs.
The major architectural limitation is that Microsoft doesn't support the FC-AL (Fibre Channel Arbitrated Loop) architecture commonly used on low-end Fibre Channel SANs. The reason, according to Microsoft, is that FC-AL doesn't allow hosts to be 'properly segregated' on the SAN. If you want to boot Storage Server from a SAN, it must either use a switched architecture or it must be directly attached from each host to one of the storage system's Fibre Channel Ports.
There are other considerations as well. Notably, the Storage Server host must have exclusive access to the disk it is booting from. This usually means using LUN masking or zoning to establish a separate logical unit for the host. However this has to be done from within the SAN since Windows doesn't provide capabilities for mapping LUNs.
If you have problems booting from your SAN, Microsoft doesn't want to hear about them. According to Microsoft, the point of contact should be the SAN vendor since the booting process is heavily dependent on the details of each SAN.
A more complete discussion of booting Storage Server, along with additional configuration advice, can be found at Microsoft Support.
Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.