If it connects to the matrix, either via wireless or a hardwired connection, they can get in. Of course, a vehicle that only accepts connections through the sat link means that they'd first have to bounce off a satellite themselves. There is a technomancer echo that allows them to use their body like a skinlink, even allowing them to link to devices that are not skinlink compatible. Meaning that a technomancer could hack into a vehicle that wasn't wireless enabled by touching it. Of course, once they were no longer touching it, they'd have to have some other means of maintaining the link.