There is no special configuration required between Cisco-----Extreme when you want to configure LAG.
Many times I have seen that LAG won't come up, you need to go to virtual interface and execute command no shut on Cisco to start negotiating LACP PDU.
I would like you to execute below command on Extreme device and check if LACP PDU's are being sent out from Extreme switch. Below command will provide RX/TX LACP pdu counter information.
"show lacp counter"
If possible check if they are able to from sharing using the static algorithm instead of LACP.
I hope this helps you,
Sumit