Remote Buddy plays extremely nice in the system. So nice in fact, that 
Apple's entire set of remote control tools and frameworks does 
recognize and address Remote Buddy's driver when it's loaded. Quit 
Remote Buddy f.ex., then go to System Preferences > Security and try 
pairing and disabling the receiver. You'll see that - even though 
Remote Buddy isn't running - the driver will act correctly and behave 
exactly like Apple's own driver. That was *a lot* of work to get 
working - and not a single bit on the system software is patched or 
modified - neither on disk nor in memory.

Regarding SageTV: 
As SageTV is currently not supported with a Behaviour, you'll not be 
able to control it out of the box. If it has built-in support for the 
Apple Remote for both Tiger and Leopard (yeah, Apple changed the HID 
descriptor for AppleIRController under Leopard which may require code 
modifications depending on whether or not the programmer knew the 
meaning of HID cookies and values), you can choose the Virtual Remote 
in the menu (=> Input devices > Virtual Remote) and control it.

You can also create an empty Behaviour with the Behaviour Construction 
Kit and assign the globally available Virtual Remote actions to the 
respective buttons. It'll then be automagically detected and handled.

At any rate, unless SageTV did something totally outside of the HID 
system, it will work with Remote Buddy just fine. The OS does, EyeTV 
does, all apps I know of supporting the Apple Remote do. The only 
class of apps that won't work with the remote under Leopard - no 
matter whether or not Remote Buddy's driver is installed - are those 
using an old version of the AppleRemoteWrapper by Martin Kahr.

Hope that helps.

Best regards, 
Felix