[@December], This is technically possible. Or at least, reading chakra and chi through firebending. It was demonstrated in season 2 of LoK. Both Water and Fire have been shown to have a healing subskill; Water mends the body, and fire can (at least) diagnose the spirit. While a firebender would be unable to freeze someone, they might be able to cure chi-blocking or personality disorders through "force of will"

[@pandapolio] That's good for us. Though keep in mind we've never seen a firebender cool anything lower than ambient temperature. Even the lava that Sozin cooled was still hotter than the surrounding air. It seems to be more akin to the techniques used to defend oneself against other people's fire, rather than bloodbending.