No, only if they are external passengers. Pages 23-24 in the 3rd edition rules talk about firing against armored and unarmored vehicles.
Thank you for Your reply, but it is still unclear:
considering again german sdkfz251, it is an open veihcle so, according to "Small Arms vs armored veihcles" rule, its crew can be fired by small arms...it sounds strange that crew of german sdkfz251 (...drivers are the most protected) can be fired on and passenger not...:what:
What do You think?