Apex has the abilities:
You cannot install non-virtual resources.
When your turn begins, you may install 1 card from your grip facedown.
[click], [click]: Turn one of your facedown installed cards faceup. If that card is an event, trash it.
Can I install a non-virtual resource face down using Apex's second ability and then turn it face up with Assimilator?
The second sentence of Assimilator indicates that Apex's second ability allows you to install things that you couldn't normally install, such as events.