Is there a relationship between event poll and class filtering (unsolicited updates)?

No, there is not a relationship between the event poll and unsolicited updates.  Each can coexist without direct impact on the other.

An event poll is a timed read of the DNP device by the Server for information on any value changes since the last event poll request.

An unsolicited update is a message from the DNP device that a particular value has changed if the item class has been set up for unsolicited messages. The unsolicited message will be sent at anytime that there is a data change in any class for which unsolicited messages has been enabled.  However, if the device supports, and is configured for, a notification delay, the message will be sent this time period after the value change.