Well, I have also noticed that various actors/actresses from Bones have appeared in Joss' work. However, I don't really think that there is a connection although you do put forth a persuasive point.

As a bit of a TV junkie, I tend to notice shows that share a lot of similar actors. Bones/JW work would not be up there on my list however, despite them sharing some similar faces. Apart from David, none of the other Bones regulars were regulars on any of Joss' works, they were only extras.

Just to pull a random example out of my hat, if you watch OZ and Law & Order (mainly SVU but include all 3 series for the point of argument) the amount of actors who appear in both (both as main characters and extras) is astounding. I have always believed that Dick Wolf (the creator for SVU and the other L&O series) was probably a fan of OZ to some extent, because pretty much every episode has an actor from the HBO show (excluding Christopher Meloni, as he is in basically every episode of SVU).

Back to the original point, it was only while rewatching episodes of Angel, Buffy and Firefly/Serenity after I became a Bones fan that I noticed that some of the actors appeared in both. Their roles in Joss Whedon's works were minor (apart from David obviously) so I doubt that Hanson would have noted their brief appearances.

I have noticed it too xP I actually grew up with Buffy/Angel, so yea I've seen all episodes, and I immediately recoginized the actors of Bones, and I think it's awesome xP I originally thought David might have had something to do with it, but reading your comment about Hart Hanson being a fan of Joss' work, I understand the connection c: And it's a great thing, he brought great actors on the show :)
I remember TJ being a laywer and being all fun on Angel, and that really cracked me up, I think it's awesome c:

just wonderin, even though im a major a buffy/angel fan and havent seen season 4 yet, which actors appreaed in which episode so i can back if so and kick myself in the face!

I actually just got through watching Buffy and Angel. I'm currently watching Bones. I, too, have noticed that many of the characters from Buffy and Angel are appearing on Bones, excluding David Boreanaz who's obviously one of the main stars. The Mayor from Buffy appears as a plastic surgeon in Season 1 of Bones. Hodgins, too, worked at Wolfram and Hart on Angel. Gunn's old gang buddy appears as a lawyer in Season 1 of Bones. Adam Baldwin (Angel and Firefly) appears on Season 1 Ep.15 of Bones. Fredric Lehne Season 1 Ep 18 of Bones appears on Firefly "Heart of Gold". That's just the first season. In episode 7 of Bones Season 2, a guest star, Kali Rocha,also worked with Joss as Halfrek, Anya's vengeance demon "friend". I'm currently watching the second season and will continue to up date this as I find more associations with Joss Whedon. Not to mention, Camille, the boss, appeared as the teacher in River's flashbacks on "Serenity". Coincidence or not, I still think it's an interesting fact that many of the same character's from Joss Whedon's shows are appearing on Bones. Whether David or the Writer/Director have anything to do with it, I don't know. Obviously Joss Whedon liked to cast a lot of the same people throughout his shows. River (Firefly) appeared as a ballerina on Angel. Captain Reynolds (Firefly) appeared as the "evil preacher" on Buffy. Zoey (Firefly) appeared as "Jasmine" on Angel. Jayne (Firefly) appeared as the new liason on Angel Season 5. "Knox" the scientist from Angel Season 5 who worked with Fred, also appeared as a vampire from the episode "Conversations with Dead People" on Buffy and on "The Message" from Firefly. As someone stated above, the idea that the Writer/Director of Bones was a fan of Whedon's work may have had something to do with casting characters from Whedon's cast members.