I've only seen the "take 10" specifically disabled for ritual checks (PH1, p. 300). Are they allowed for Aid Another?
Technically yes, in practice usually no
From the RC, p127:
Nothing in that list forbids you from taking 10 when you aid another. It does, however, ban taking 10 in most of the situations in which you would actually want to use the aid another action, skill challenges in particular.
Technically, you can use aid another to provide an ally a bonus on an attack roll. This is almost always a bad idea. If you were to do this, however, you could not take 10 because attack rolls are not skill checks and you can only take 10 on skill checks, in addition to generally being rushed and threatened in situations wherein you are making attack rolls.