CAN you depart "IFR" from a non-ATC airfield, anyway? You can't be in receipt of IFR departure instructions, for a start.
The originally described scenario is perfectly OK for a departure, whatever one calls it, provided the pilot is capable of instrument flight. If not, he almost certainly won't get very far.
The additional risk (relative to departing from the same place in say a higher cloudbase) is that in the event of a SEP engine failure one won't have much time to look for a field. I departed from the Scilly Isles once in probably 200ft cloudbase but there is only water at the end of the runway...