Deliver Aid (Ex)
[...]
This ability replaces speak with animals of its kind.
[I]mproved familiars do not gain the ability to speak with other creatures of their kind [...].
http://www.d20pfsrd.com/feats/general-feats/improved-familiar
Can an Improved Familiar take the Valet archetype?
The Valet archetype is not the only one that replaces that ability, so this question applies to more than just that archetype.