These images are taken from the festo QS specifications and clearly state these connectors are designed for vacuum as well as pressure.
-.95 bar and up.
While it's true the tube must be cut well, rigid and especially must not make sharp turns right after exiting the connector, I don't see how it can be claimed these are unsafe for the suction side.
I've been using one before the UAT and one between UAT and pump on each airplane for the past 4 years and so far never had any issues (up to 180N).