How do you know if sausage is cured?

Most all fresh Italian sausages made for spaghetti or for general cooking are just fresh sausages and not made with any cure; and you can smoke them as long as you have your temp at 225° in your smoker and you get them from 40° to a minimum of 140° within 4 hours, and that should be very easy to accomplish.  You want to cook them to a minimum of 155° - 160° for them to be done, or finish them on the grill or in a pan to that temp.

Also, if it's fresh meat, if it has cure in it the color will be a heavy gray, not pink like fresh meat.  Fresh polish sausages that you purchase at Easter is a good example, it almost looks spoiled; it has cure in it so it can be smoked long and slow.  Anything with cure in it turns that color quickly; it is so surprising at first that it will become uniformly pink all the way though like ham!  It goes from gray to pink!  

Fresh sausage, on the other hand, is the reverse - it turns from fresh pink to cooked gray throughout - any pink left in the center, it's not cooked all the way through!

It would be on the package.    Fully cooked sausage just needs to be warmed.   If nitrites where used you can cook it at a lower temp for a longer period of time.   If the sausage comes out of the fresh meat counter don't bet on it being cured and you should probably cook it at a higher temperature for a shorter period of time.

I don't feel comfortable giving times and temps without knowing what you have.