Polyatomic molecules like HCO can exist as negatively charged anions or as positively charged cations, or as neutral free radicals. All three exist and are well-known, and very reactive, species.
The Lewis structure for formyl radical (HCO) illustrates that this radical has one unpaired electron on carbon and is therefore predicted to be very reactive. If it loses this unpaired electron, it becomes formyl cation (HCO+), but if it instead gains another electron it becomes HCO- anion.
Following the usual rules for determining formal oxidation state, the O atom is -2, H atom is +1, and total of all atoms is equal to the total charge on the molecule. Therefore, the oxidation state of carbon is
0 in HCO- anion
+1 in HCO radical
+2 in HCO+ cation
Therefore, the oxidation state of the central atom is related to the total charge on the molecule, but not equal to it.