Joel and Phil

Joel Dawson and Phil Argus are the main characters of the Flash animated web series Bonus Stage created by Matt Wilson. Like Space Tree, this series was picked up and hosted by Keenspot. The two series ran side by side and shared a lot of audience overlap.
While the Bonus Stage series was running, Keenspot were advertising a game called The Saga of Ryzom in their banner ads. Part of this advertising agreement seems to have involved video ads, as an ad for the game featuring Joel and Phil was created by Matt Wilson which would load at the beginning of certain Bonus Stage episodes. When going to these episodes a separate Flash file called bsload.swf would load featuring the ad. Once the ad was over, the .swf file for the actual episode would load. The ad was sort of a meme in the Bonus Stage community, and was parodied elsewhere in the series.
In late 2004, a page was created on the Space Tree website called Seasons Greetings To You! It featured a bizarre interactive bit of Space Tree weirdness, however, before that content loaded a copy of the bsload.swf file renamed spaceload.swf would play, featuring the same Joel and Phil ad for Saga of Ryzom. It's possible that Keenspot had asked Ed Atlin to place the ad in front of one of his episodes of Space Tree, but not wanting to do so he instead fulfilled the obligation by placing the ad at the beginning of a weird easter egg on a page probably no one would see. Or maybe the ad was just meant to annoy whoever found the page? Who knows. 
So yes, Joel and Phil never actually appeared in an episode of Space Tree (although Space Tree and the Commander featured several times in Bonus Stage), but they did technically appear in some obscure thing to do with Space Tree, and apparently that's enough to get them their own article on the Space Tree wiki. Go figure.