Can polyatomic ions (CO₃, PO₄, SO₄, NO₃) be considered conjugated systems? From my perspective these resonance structures allow these specific polyatomic ions to act as donor-acceptor molecules. Many donor-acceptor molecules also tend to be conjugated systems because they have chains of alternating conjugated &#x3c0; orbitals. 

So does this imply that these ions (due to their resonance structures) can act as though they had a conjugated system or am I making too big of an assumption?

Curious on others perspectives/if I'm totally of my rocker.
"Conjugated" implies a 1,3-shift to move an electron or hole.  It is a remnant of LCAO modeling that is obviously wrong but fantastically useful short of the Woodward-Hoffmann rules.  I'm not sure inorganikers would like the name as such. MO modeling is accurate but unwieldly.  "Delocalized" or "resonance hybrid" is good, certainly for inorganic systems that may have (virtual) d-orbital participation.

Consider nitrate.  Inorganikers would say $\ce{N^{5+}}$, $\ce{^{-}O-N(=O)2}$, with five bonds to the nitrogen.  The negative charge 1,3-shifts around all three oxygens.  Organikers would see it as $\ce{N^{3+}}$, $\ce{[^{-}O{}-]_2N^{+}=O}%edit$, with four bonds to the nitrogen.  1,3 shifts, etc.  Is nitrate ever a bidentate ligand?  YES!  But it is just another resonance structure.

Inorg. Chem. 35(24) 6964 (1996) 
http://pubs.acs.org/doi/abs/10.1021/ic960587b