Well as another engineering type I would say its completely dependant on the engine design and component design about what's going to happen.
For some it won't be a problem and others its going to break something.
BTW the ability of vacuum pumps to be turned the opposite way only really holds with new ones. Mid life units which have only been run one way your asking for trouble mainly due to wear profiles and material properties changing. Normally you will get gradual wear but one turn in the wrong direction and you "might" get bigish lumps coming off instead of the normal dust wear erosion.
As for the aero engines what may be ok in a normal utility engine with no inverted capability might do some quite nasty damage to an engine with inverted flight certification. Aero engines will have none return valves where as car engines won't in various systems. So I do actually agree with everything Icepaq says about consumer car engines.
But for me it is quiet dangerous to the wallet to presume that they translate directly to aero engines. All it takes is one none return valve to operate as per design and you have issues. Gravity time flow isn't an issue, but as soon as you get about the valve operation threshold then your into outside design operation.