I know Brocade will gladly accept CDP from Cisco devices and display it in a show fdp neighbor
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If you enable CDP on a Brocade chassis will it send CDP packets out as well as FDP?
As far as I know, you can only tell Brocade to intercept (i.e. be able to understand) CDP or not (i.e. forward them along). If you have CDP off, then they will be forwarded on and won't show up in a show fdp neighbor output.
If you are mixing vendors, I would recommend that you look at having them all run LLDP if possible.
Unfortunately, Brocade gear will not send out CDP packets for Cisco gear to understand. Brocade gear only transmits FDP, but it will be able to understand (most of) the information in CDP packets if configured to intercept them. Enabling CDP on a chassis only configures the device to intercept CDP packets.
Your best bet (if all equipment is under your control) is to configure LLDP between all devices in a mixed-vendor environment.