from what i understand, yes, you can still get updates from ATT if the device if rooted and you retain the current carrier issued ROM.
i'm rooted and i received the last JH7 update but since then i've removed the ATT bloatware. i'm curious to see if the supposed upcoming froyo update will take with the bloatware removed (***keeping fingers crossed***).
if a froyo OTA update does take, you should expect to lose root access and have new bloatware installed.