Question
Can I use UREA alone to fertilize my lawn. If indeed, what is the correct setting to use for scotts spread 1000? Please advise.

Answer
Unless the fertilizer requirements recommended for your lawn specify a more balanced fertilizer, I see no conflict.
To get specific recommendations from Scotts, go to URL:
http://lawncare.scotts.com/index.cfm/event/ContactUs.showForm
and ask for settings.
I use basic math to figure out the spread rate.  Find the setting recommended for a known fertilizer (on the bag usually as per brand of fertilizer.)  Find the rate recommended, lbs. per 1000 sq. ft.  Assume that the urea is the same density and adjust the rate for # lbs./1000 sq. ft. (or M.)
For intance, if 16-4-4 is applied at 12 lbs./M, that is 2 lbs. of N/M.  Find the analysis of your urea, and apply a suitable amount to produce 2 lbs. of N/M with the setting which will drop the correct percentage of product on the lawn.
If you have doubts about your calculations, apply half the amount by your best figuring with one application and watch the results.  
If you are sure about your calculations, cross the lawn in in both directions, applying the one half per pass.
Best of luck.