That makes sense, physics-wise.
Sorry, not for me.
As the cut is unidirectional and in the pulling mode (the chain doesn't allow to be pushed), only the main engine has a direct effect on the cut and is in the right place to sustain the main strain of ripping the wood.
We can see different cases :
If the "tip" engine is set too low on the rpm's side, the main engine has to pull both the chain throw the wood
and the secondary engine to speed it to its own level. In this case you clearly loose power.
If the "tip" engine is set exactly at the same speed, it does nothing else aside accompanying the main engine, maybe pulling a little the chain on the back side. Very kind of him, but I can't see that as a gain.
If the "tip" engine is set at a little higher speed, then yes, it actually help to cut the wood, because the chain is in tension all the way from its socket to the entrance on the cut.
If the "tip" engine is set too high, then it does all the work, and more than that, it has to pull the main engine faster. So you fall back in the first case.
It must be a sweet spot to get the most power of the both saws, but I guess it could be difficult to find and to follow during the cutting process.
That's the way I see it, maybe I'm wrong. It should be easier with a reversed differential mount or a hydraulic transmission, but it's far out of the subject.