immigration and labour laws are regulated by the federal government, although each emirate is entiled to administer and "bend" them according to its own requirments. under the labour law if a business is regisered in dubai its employees are supposed to be registered with the labour department of th emirate of dubai - the same applies to sharjah, RAK etc.
in the case of any greivences they have to be lodged with the labour department of that emirate (as the local interpretation between the emirates does often vary - as mentioned above). in addition businesses registered in a particular emirate are given a labour quota by the department of labour (of that emirate), this is the amount of people that they may employ, the "quota profile" follows the regulations currently in favour by that particular emirate.
in some instances where a large company may have a number of registered branches - crossing a number of emirates they do sometimes swap or exchange employees, although this can cause problems if they had a labour inspection. you may find that if your company is registed in both sharja and dubai some of the employees were empoyed on thier dubai quota and the balance on the sharjah branch quota - if one is full they are forced to make use of the other.
you won't be able to get an alcohol license in sharjah, and probably not in dubai either as you have to provide your passport and residency stamp in the application to the police department.
the vehicle i don't think there is a problem, but am not certain.
hope this helps and doesn't confuse the issue more
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