No a BLE can not discover a classic bluetooth device nor a classic bluetooth device can discover a BLE.
A device with BT V4 will discover both.
And A BT V4 will be discovered by BLE if it is advertising as BLE.
I also had same question, so I did little experiment.
I may contribute to this topic from my experiment that I did with old mobile(Nokia C5-00), New mobile(Samsung galaxy grand prime) and two bluegiga ble113 chips.
I swithched on bluetooth of all the devices and started scanning for near by devices I observed the following:
Observation1: Samsung galaxy grand prime (BT version 4 +Ble): It was showing both bluegiga ble113 chips, and Nokia C5-00 on the list.
Observation2: Nokia C5-00 (Earlier version of BT): It was showing only Samsung galaxy grand prime in the list.
Observation3: ble113: Out of the two ble113 chips one was in advertising mode and other in scanning mode at first the scanner chip was discovering only other BLE113 advertiser chip, but when I started advertising from Samsung galaxy grand prime phone using BLEBroadcast app the ble scanner chip started discovering the Samsung galaxy grand prime phone also.