Yes.
It's probably not harmful abuse, but it's still abuse.
Abuse does not necessitate using something wrongly. You can abuse privileges.
If you do *anything* in game that you could not otherwise do if you were not the admin and has an impact in the world in any way, you're abusing the power of being an admin.
Of course, if your server title is "Prebuilt towns and housing" or something, then people will be connecting expecting that specifically, and it wouldn't be viewed as abuse necessarily.
You may be viewing it as not effecting the game, but consider this: part of the game is surviving long enough to build your shelter. If I stumble upon a prebuilt house and all I have to do is put a door on it, I'm bypassing a large portion of the "early game".
I completely disagree. Saying that doing anything you wouldn't be able to do if you weren't an admin is abuse is just plain retarded. Might as well say that banning and kicking is abuse, since regular players can't do that. Admin abuse implies "abusive" behavior, and I fail to see how building a shelter town for everyone on the server to use is abusive. It's not beneficial to the admin in any way, and isn't targeted towards any particular player.
If people dislike the way he manages his server (although I'm not sure why anybody would be annoyed by random "neutral" buildings), they're free to go somewhere else. It's more of a server feature than anything else.
Somebody needs to go read the definition of abuse. According to wikipedia, it is "improper usage or treatment of an entity." Spawning neutral buildings that don't benefit or penalize any particular player, or the admin himself, can hardly be called improper usage of admin powers. It's just a way of running a server.