Well, provided that it doesn't pull more than the current allowed to drive a USB drive on a keyboard port ("unpowered") .. it will work on the keyboard.. This means it has to work on 250mA or less... The computer's direct USB port on my iMac for example provides at least 500mA to power an unpowered device (hence two ports on the keyboard divide that down to 250mA each or less)..Check the product power requirements to know what you can get away with.. To find out how much power your computer is supplying to your USB ports, look in System Profiler (OS X Apple menu, About this Mac, More Info...)
Worse to worse you can get a "power injector" to add power at the port on the keyboard by plugging in an AC
C converter into a special USB plug which marries that to the data from your underpowered port to make a hungry device happy.. now add a port splitte to that and you have yourself a powered USB hub.. lol..