Can 61F Floatless Level Controllers be used only for liquid level detection in order to output a signal?

Yes, this is possible by disconnecting E2 self-holding circuit.
However, when there are waves on the liquid surface, 61F will also repeatedly turn ON and OFF, so the lifetime of the contacts will be shorter than usual.

61F-G Example

Applicable Models

61F-G/61F-GH/61F-GD/61F-GR/61F-GL 2km/61F-GL 4km/61F-G-TDL/61F-GT
61F-GN/61F-GNH/61F-GND/61F-GNR
61F-GP-N/61F-GP-NL 2km/61F-GP-NL 4km/61F-GP-NH/61F-GP-ND/61F-GP-NR/61F-GP-N8/61F-GP-N8L 2km/61F-GP-N8L 4km/61F-GP-N8H/61F-GP-N8D/61F-GP-N8R
61F-UHS/61F-GP-N15/61F-GPN-BT/61F-GP-N8HY