Can I get a feedback signal from the CEE plug and socket?

Yes, for 63A and 125A receptacles and plugs and connectors, this can be done with a so-called pilot contact switch or a PCS (PilotContactSwitch). (Pay attention to the “P” index for the part number)
Pilot contact: this involves another sleeve being added to the internal wiring, which uses the standard pin on the plug to establish a lagging connection.
PCS: this involves a switch being installed in the internal wiring. It is a normally open contact with no potential, which is mechanically provided with a lagging current via the pin in the plug.
In both cases this has to be requested when ordering; retrofitting is not possible.
With some types of 16-amp and 32-amp receptacles it is possible to install an auxiliary switch: part no. 41000 (retrofitting possible). Relevant appropriate receptacles are listed in the MENNEKES catalogue.