Are shimano FH-2200 hubs strong enough to use in a tubular wheel for CX racing?
Yes, I would suspect they are just fine. These are relatively inexpensive when new, and require little maintenance if broken down and lubed once in a while. 

What really matters in cyclocross is the number of spoke holes and flange geometry of the hub. I just did a quick google and found FH-2200 hubs have beefy flanges and 36 spoke holes. I was not able to find any other configuration. 

I've more often than not found wheel failures at the spoke junctions (hub, rim) or the rim itself. I've very rarely seen a hub fail that has been properly maintained. 

So, my answer is this: they should be fine. Lace them up in a 3x pattern with a decent rim and enjoy some cyclocross!