On Reader Mail, The Acceptable DMPC?
Nope, a Dungeon Master Player Character is never ok.
What you are talking about are services NPC's, henchmen, and hirelings can provide. This is different then a DMPC who is a character the DM rolls up to play.
Will the DM make a ruling that will restrict his character's power? Is the party willing to not only wait on the DM to reply to their actions, but spend a portion playing the game by himself? Will the DM resist being able to show off how smart he is by solving his own puzzles? Does anyone have patience for the overwhelming narcissism of a person who not only wants to run a game, but also be the most important character in it? How could it be otherwise, being that he is literally being played by god.
The NPC and Hireling? Controlled by the player, untrusted, subject to morale, is a different situation.
The last sentence of your letter is telling of your background. The appropriate response to them not rolling up a lock-picking thief or healer is that they don't get to pick locks or heal.