Remote Buddy doesn't do anything by itself to prevent sleep unless you 
press a button on your remote.

What may be a problem specific to the Keyspan IR receivers is that:

1) the Keyspan IR receiver will wake your Mac (and possibly also keep 
it awake) in case it receives any kind of IR signal / light for a 
short period of time. In some cases, bright, hot light bulbs may 
already be sufficient (I could watch that phenomen a few times).

2) OS X needs to be expressly told to pay attention to wakeup events 
coming from the receiver. In order to allow you to wake your Mac via 
your remote, Remote Buddy's driver tells OS X to pay attention to 
that. What it does not have any influence on, though, is when and on 
which events the Keyspan IR tells the USB port to wake up. That's a 
hardware and OS X USB stack feature.

You may try with the IR receiver unplugged or "covered" with a book in 
order to see whether that's the problem.

Other than that general physical / hardware problem, that can't be 
resolved in software (other than to completely drop wakeup support for 
Keyspan IR receivers - which AFAIK is only supported by the Keyspan 
Express IR receiver, btw), Remote Buddy certainly won't keep your Mac 
from sleeping.

Best regards, 
Felix Schwarz