Depends on if the Prophets are taking forms or just being seen in them, no? @Christopher mentioned some time back that he took the Prophets' appearance as being more of a "person seeing what their brain is making them see because the true form can't be comprehended" thing (if I remember right), like the Q Continuum, or like Galactus in Marvel, and I kind of liked that interpretation.
I think that's pretty clearly what Michael Piller intended. After all, the wormhole aliens' avatars mostly only appeared in the contexts they occupied in Sisko's memory -- he didn't just see Jake, he saw Jake at the fishing hole or the baseball field, and he didn't just see Locutus, he saw Locutus on the viewscreen of the Saratoga bridge. For the most part, even later on, that was usually the way people experienced the wormhole aliens.
It's not the same as the Q Continuum, though, because in that case, Q (or Quinn) was responsible for creating the illusion for the benefit of human observers. For instance, Quinn chose to represent the Continuum as an arid wasteland because that was what he felt it had become, and later, Q chose a US Civil War setting as a metaphor for the Q's civil war. In the case of the wormhole aliens, they weren't doing it deliberately; after all, they didn't even know what Sisko was when he entered their realm, or how human memory and time perception worked (not in Piller's original conception, anyway). What he experienced was just his own mind scrambling for analogies in its own memory to map onto what it perceived, in the absence of other sensory input.
And if that's the case, then the Collective might very well just see their true form, not a mental interpretation, since it actually can probably mentally handle it.
I don't think their true form is something that can be seen. If they existed in a realm that followed our physical laws and had bodies that reflected light, then Sisko could've perceived them and his brain wouldn't have needed to make analogies. Besides, time doesn't exist in their realm, so how could light or sound travel and bounce off of things? It's not about "handling," it's that there's simply nothing to perceive in the conventional sense.
I think the most literal representation we've seen of the wormhole aliens' realm is the pure white void that people perceive before and between the visions. The visions are what they sense mentally when the Prophets communicate with them. Basically they're in a sensory-deprivation environment, so the imagination takes over and creates hallucinations to fill the emptiness. I don't think Borg drones would be permitted imagination. Any such distractions from their role as cogs in the machine would be suppressed -- as would their memories of their past lives, so there'd be little to draw on for the creation of analogies.
I think that the Collective would perceive the Prophets much as it presents and perceives itself -- as a faceless chorus of voices, a non-localized consciousness.