This is always a problem when a company is purchased by one of the vendors it sits above in the value chain, esp when impartiality and independence is important in a space such as vendor monitoring.
I can't see RS buying CloudKick for internal monitoring of its own customer's servers and instances because they would already have a mature solution by now.
I'm not sure I want to be providing RackSpace with performance data of my servers running on their competitor's instances, the CloudKick agent is placed to send (albeit transparently) all sorts of data back to RS. And don't be surprised if other vendors raise concerns to this effect too.