depends on the failure mode
capacitor failures:
if you mount it vertically, the leads may stretch under vibration
and the actual capacitor inside the case may be stretched also
and it will jump up and down
if you mount it horizontally, you can put a strain relief in the leads
but you'll need to glue the case to the board somehow
then the actual capacitor inside can bounce back and forth inside the case
in either direction, the leads can break
since there is no information in the data sheet about vibration or shock,
i suggest you do the test
mount two or three vertically and two or three horizontally on a typical pcb
they would be mounted on in your machine
test their electrical properties, vibrate in one direction and test again
repeat in the other two axis
vibration test should be at least 20% greater that the vibration you expect
if they pass, vibrate them again at 50% greater, etc
then you'll know
you might also vibrate a set of aluminum electrolytics at the same time