I'm not sure if this is the correct site to ask this
Question, if it is here goes, if not please direct me to
One who could answer this.

Are truck drivers who travel interstate federally mandated
To wear seat belts while driving their trucks?
Is there a weight clause with this requirements?

Yes, truckers must wear seatbelts. Lapbelts actually. Shoulder belts are not mandatory. For more info go to:

I do not believe there is an exclusion for weight.

http://www.michigan.gov/msp/0,1607,7-123-1586_1710-90103--,00.html

Buckle up!

Yes. We have been federally mandated since I began driving in 1982. There is no special clause regarding weight.

From the Michigan site linked to by Viking:

"While vehicles over 10,000 lbs. (Gross Vehicle Weight Rating) are not required to be equipped with a shoulder harness, these vehicles must still be equipped with, and drivers must wear, a lap belt. "

Yes, they must wear seatbelts and their passenger must wear a belt as well. They are liable to get the same tickets written for no safety device as a regular license holder gets.