The columbium jet nozzles themselves can take the heat, but "penetrations" of the spacecraft heat shield are a definite potential failure point, including penetrations for the Reaction Control System (RCS) jets. The design to preclude hot gas intrusion while preventing damage to the surrounding Thermal Protection System can be quite complex.
The forward RCS provides attitude control and small velocity increment
translation from main engine cutoff during ascent until the entry
interface. It includes 16 radiation-cooled thrusters (14 primary and 2
vernier), made predominantly from columbium (disilicide coated except
for the injector plate), and fully exposed to aerodynamic heating.
Surrounding HRSI tiles of the TPS have been partially replaced by
other materials. Insulation-filled metallic plume shields are placed
downstream of long scarf (primary -Z and -X and vernier) thrusters.
High density (22pcf) RSI tiles form the TPS in narrow areas between the
-Z, +Y, and -X thrusters. Thermal barriers serve to block gaps between nozzle exits and adjacent TPS from boundary layer gases. Other thermal
barriers are required between the plume shields and surrounding tiles.
Each thruster is housed within a cylindrical titanium container that
seals the internal compartment from the exterior environment. The
design is complex.There are approximately 20 maximum temperature
limits to be observed, many with several variations associated with
position, mission phase, or frequency of occurrence. The primary
downfiring (-Z) thrusters experience the most severe entry heating. A
section through the downstream edge of this installation is shown in
Source SHUTTLE TPS THERMAL PERFORMANCE AND ANALYSIS METHODOLOGY
(image source, annotated)
Example thermal barriers:
HRSI - High-temperature Reusable Surface Insulation (aka black tile)
RSI - Reusable Surface Insulation
SIP - Strain Isolation Pad
TPS - Thermal Protection System