Tactics is semi-canon (major events canon, some details non-canon), as for the Fallout Bible, they follow some parts pretty closely, like the timeline, but ignore some other stuff, e.g. how GECK works. As for Van Buren, they have been using some ideas from there in Fallout 3 and its add-ons, and nothing in Beth's FO3 contradicts Van Buren lore, but they have never officially declared any of it canon or non-canon. I suspect that the makers of New Vegas will use even more Van Buren lore.
Yeah, I think if Bethesda were to make an official comment on the matter they'd only consider work in published materials to be canon - but for most intents and purposes the Fallout Bible is considered canon. They probably feel similarly about Van Buren.
While one could argue that Bethesda is the only one who can truly tell us what is and is not
canon I've always felt this is really an individual choice. Using the Elder Scrolls as an example, there's been a lot of stuff that is not actually official but has involved current and former developers: stories released on the web (particularly by MK), a number of semi-RP threads in the Lore forum (most famously the Trial of Vivec), and even Loranna's long running RP. While none of this is
canon by Bethesda's accounting it is 'real' enough for plenty of fans. Ignoring for a second that some of this material has been put in or alluded to in later published work, if these fans want to consider it canon for their view of the Elder Scrolls then that's what they should do!