in addition to being an unsupported configuration presently, as far as i know it's never been tried. you may want to sidestep the issue entirely by hard-coding the BL_AS and BL_AP variables into the boot images. this should work well to avoid the DHCP issue provided you're not consistently changing your appservers that BMI needs to talk to.
This is exacly what I did. The nortel netid dhcp server does not work well with either blade.img or tweaked_network.img, or a winpe image for that matter. Although we finally have the nortel dhcp configured to give out the blserve and blport, all images seem to hang sooner or later. I hard coded the BL_AS and BL_PS inside init.bat of a WinPE image and it works wonderful.