Hi,
I think, no cert for this test is definitely reasonable. OOAD with UML is just standard knowledge for software development. It can be used together with development paltforms from IBM, Microsoft etc. but it's not theirs.
So there is no point that IBM will reward it (alone) one Big Blue certification (even it is required when you want Solution Developer cert).
But anyway, we should thank IBM for their effort to maintain such a good exam. They took the risk of developing a standard technology unbiased exam for software developer world, which I've never found from Microsoft, Novell or Cisco (well, I guess that IBM gains very little in this exam registration fee)