To answer to your second question first
They always did back in the days of the old Sporting Globe (the pink paper)but for some reason known only to themselves decided to stop doing it back in the 1980's (probably due to lack of staff as the trots was starting to go into decline and they cut back on their coverage).
Q1.The weight or the driver has very little effect on the performance of a pacer or a trotter because of the momemtum. An example of this was a pacer by the name of Garrison Call trained and driven by Russell Fiddler.
Russell tipped the scales at around 25 stone(about 160 kg) yet he won a lot of races.One night at the showgrounds they put Brian Gath in the gig and all the smarts sent him out odds on as Brian was only a lightweight(about 60 kg) they said he couldn,t lose. Led and duly got run down in the straight after having an easy run in front.If ever there was a case of weight making a difference that would have to have been the case to prove it but it didn,t.
p.s. Brian Gath was the driver who started the swinging in the sulky after he went to the states for the world driving championships as it was pretty much the standard way to rive over there.