the only thing i've seen brick a phone from flashing is a radio or a bootloader. luckily there arent any of those available for these two phones.
If you use the software update on a stock rooted rom, you could get a brick that way. If anyone can figure out how to get these phones to boot into fastboot without erasing the boot.img i've found that you can boot a recovery from fastboot quite easily. Just need the button combo to boot into fastboot and then i can post how to use fastboot for anyone who wants it.
so far the only way to enter fastboot mode that i know of is to boot into clockwork mod recovery, go to mounts and storage and format the boot partition. reboot and you have fastboot mode.
I know you can boot images from fastboot, not sure about flashing them as of yet. testing that out tonight