Here we'll deal with games that are not DKU but which are in some way referenced in DKU games, be them references to the actual in-game continuities of these other games or references to the other games as just... games. Still with me? Good!
3A: References to the Sabreman Series
Okay, bear with us here: Sabre Wulf GBA is not DKU. We know this. But it's one of the more important entries in the whole Honourable Mentions oeuvre; Banjo-Tooie famously featured the re-animation of the Sabreman character (frozen in time—or to put it more accurately, ice—since the '80s) thereby definitively linking Sabreman's world with the one we explored in Tooie. So not only does the Sabreman series take place in the same universe as Banjo et. al, it probably takes place in the same postal code. As a series it's about as close as you can get spiritually to that nebulous "DKU feel" but if that's not enough for you, Chad said I should put these on here, SO THERE. This section tackles Sabreman's history both pre- and post- Banjo-Tooie, since we're considering the series as a whole to be "referenced in the DKU" rather than any individual game.
3B: References to Other Games
Background gags and cheeky side-references are the order of the day here, and the DKU is replete with them (usually when Rare are involved - they can't help themselves, it's like an illness... but, you know, a fun illness). The sphere of coverage for this lot is a bit hazily-defined and open to interpretation so if there's something we've left out, blame it on spheres.