The sensor can serve out events in both formats simultaneously.
Version 4.x sensors stored events in the older RDEPv1 format, and could only server events with the older RDEPv1 format.
Version 5.x sensors instead store events in the newer SDEE/CIDEE format, and will natively serve out these events in the SDEE/CIDEE format using the sdee-server web service.
However, to ensure compatibility with systems designed for 4.x with the RDEPv1 format, a converter was also included with the 5.x sensor. When the event-server web service is connected to (instead of the sdee-server web service) the sensor will automatically internally convert the natively stored SDEE/CIDEE formatted alarms into the older RDEPv1 format and serve them out.
So yes a RDEPv1 style client can connect and receive events from the sensor at the same time that a new SDEE/CIDEE style client connects and receives events from the sensor.
NOTE: CIDEE contains the Cisco specific parameters that are added on to the standard SDEE format. SDEE/CIDEE may also be referred to as RDEPv2 format.
Specifications are available for download from:
http://www.cisco.com/cgi-bin/dev_support/access_level/product_support?pcgi=1&product=IDS_INT_API