1) The tougher, armored skin on their heads and backs will be resistant to bullets but not render them entirely impervious to damage, much the same as the bruising caused if someone takes a bullet while wearing bullet-proof armor. The loud noise and impact will startle them, but they will quickly learn to adapt, including learning what a gun looks like and how best to avoid being shot while still pursuing their prey.

2) They are nocturnal in behavior, but are still functional in low or bright day light, so changes in light won't bother them. There will be some standard caution regarding fire.