This is nothing to do with inversion, verbs, or subjects. It is about adjectival phrases.
First, in case you are unclear, demands is a (plural) noun in this sentence.
Normally, an adjective (including a participle used adjectivally) precedes its head noun in English:
But when the modifier is not a simple adjective, but a phrase consisting of an adjective with some sort of complement, the phrase often follows the head noun:
demands [collected from the field team]
(In this construction, the adjective is most often a participle, but not always, eg a parcel ready to go.)
So in your example, the normal order is
demands collected from the field team.
Your alternative is grammatical, but has a different structure, and possibly a different meaning:
[collected demands] [from the field team].
It is not specifying that the demands have been collected from the field team, but that the demands have been collected, and that they are from the field team. This might be the same, but it might not. When collected is used a simple adjective like that, it tends to have the meaning of "collected together, eg by an editor, for publication or study", rather than its basic meaning of "brought together".