It would have to have iterative attacks at least.
As Otu said - the differences are mainly in the details. And I think most DM's would simply play them as manufactured weapons anyway, unless you specify exactly what the differences are. For example, if the Drenkari instantiates a spiked chain and makes a trip attempt... could it drop the chain to avoid a counter-trip? If it instantiates a longsword and its opponents tries to sunder it... does the sunder simply fail with no explanation, or could the sunder actually damage the drenkari?
It would be a lot easier to say that it manufactures its own weapon, and as soon as the weapon gets separated from the drenkari it falls apart into its constitutive swarm creatures and immediately rejoins the coalesced form.
On a related topic... I suggested earlier that perhaps it would use a different - possibly random - weapon on every attack, implying that it would take effectively no time to switch weapons. At the other extreme, we could say that it takes a Move action or more to instantiate a new weapon. Where do we want to fall on that continuum?