It sounds like you are adding a transfer switch to an existing building and you want to run wires coming off of the service disconnect to the utility side of the ATS and then bring wires from the common on the ATS back through the same conduit. If this is true then the answer is yes.
It would be ok if this is what he had but I dont think it is.
To me he has a meter only on the outside of the building probably going just inside to a Main Breaker Panel.
He's wanting to add a Transfer Switch on the outside next to the Meter, Take the existing wires off the load side of the meter that are now going in to the existing panel, route new wiring from the load side of the meter to the line side of the new transfer switch, then, take the load side wiring from the transfer switch back into the meter can and splice on the the existing wires that feet the existing panel.
If this is the case, I say No.
You'd have service conductors and feeder conductors sharing the same raceway between the meter and the Transfer Switch.
