In most cases; yes. That depends on the humidity of where the car is going to operate. If the environmental conditions are harsh, the speaker membranes must cope with it. Stereo-speakers, generally manufactured for indoor use might not.
Yes, if you keep a couple of things in mind. The first is generally the ohms rating of the speakers. Most home speakers are rated at 8 ohms impedence, while car stereo speakers are rated all over the...