Hi Johan,
As far as I know, DHCP requests are a way to "gather" devices information, but in order the device to appear in the NAC Control, you have to configure your current switches with -at least- RADIUS MAC Authentication on the your wired access ports (and in the EAC you create an "always allow" rule, that reply with "access-accept" messages to your switch), this will help you having the visibility. Pay attention to set a "Fail-safe" policy on your switches so that in case of EAC engine failure, your wired access can keep on working.
Regards,