Two feats in Races of Stone have as one of their prerequisites being a whisper gnome. This made me wonder: Does a whisper gnome count as a (generic, untyped) gnome for meeting prerequisites or is whisper gnome an entirely different race from (generic, untyped) gnome and unable to meet (generic, untyped) gnome prerequisite?
All gnomes have a subrace like rock or whisper
There's no such thing as a gnome without a subrace. Although not called out as such by the Player's Handbook (16-17), the gnome race described therein is the rock gnome, "the most common variety" of gnome (Monster Manual 131), and the game includes a fairly large number of gnome subraces, yet the larger classification—the gnome race (and, perhaps, kind, what PH 310 calls a "subcategory of creature")—encompasses all gnomes in its warm, gnomish embrace.
This means both a whisper gnome and a rock gnome and any other kind of gnome are all broadly gnomes. This also means a whisper gnome can meet the prerequisites of feats that include gnome and whisper gnome, but a whisper gnome can't meet a feat's prerequisite if the feat's prerequisite were rock gnome like the feat Rock Gnome Trickster (Races of Faerûn 167). (Also see this question.)
Just in case further proof is needed, the Exemplars of Evil NPC Draen Ralgael is a wererat whisper gnome rogue whose subtypes include gnome (52-3).
Having the gnome subtype would be sufficient for whisper gnomes to qualify as gnomes for feats and prestige classes. Races of Destiny talks about how the human subtype would do this for half-human races, and certainly all the elf subraces in Forgotten Realms can use elf feats and prestige classes.
The problem is that we don’t have any example whisper gnome statblocks, which means we don’t explicitly know that it has the gnome subtype. I think it’s only reasonable to assume that they do, but nothing comes out and says it.
Also, for the record, the race listed as “gnome” in the Player’s Handbook is actually a rock gnome. The Monster Manual (i.e. also core) includes the forest gnome as well. Both have the gnome subtype, and the rock gnome, clearly, meets any “Gnome” prerequisites. The forest gnome should as well, and thus I’d say that whisper gnome also does.
As far as consensus, whisper gnomes are widely recommended online for stealth; their racial features are excellent for it. No one in these discussions considers them restricted from taking gnome-only feats and prestige classes. In the Shadowcraft Mage Handbook, about a gnome-only prestige class, both whisper gnomes and forest gnomes are considered (in this case, the forest or rock gnomes’ +1 to Illusion DCs generally trumps anything that whisper gnomes offer, but still, no one was saying you can’t). And certainly in any discussion of racial-specific options, consideration of subraces is often an important part of the conversation.