Do any dynometer's find the weight of the vehicle?
 

Do any or maybe do all dynometer's figure the weight of the vehicle? If not how can they give even a close estimate of the rwhp?

I don't believe dynojets do. Mustang dynos do compensate for weight by increasing or decreasing static force to the rollers, depending on what the car weighs. It doesn't figure the weight of the vehicle, you have to put it in manually.
And, a mustang dyno will also increase static force the faster you turn the rollers to simulate wind resistance.

So dynojets can't be put in manually? just a mustang dyno.

Correct. Just another way to manipulate Mustang dyno readings. Like weight really has any affect on whp.