The only thing I'd be concerned about using a solid pin is expansion. Perhaps the roll-pin expands inwards when it gets hot, whereas a solid pin is going to expand outwards and stress the balancer and crank. I'm no thermo-dynamic engineer, so I could be way off base. Those little roll-pins are pretty sturdy though, I can't see them being too weak to do the job.
An important note is that the shear force applied to the pin is longitudinal, not perpendicular to the length of the pin. If you look how the holes are drilled, the hole is half-way in the balancer, half-way in the crank. I can't imagine the force it would take to make one of those pins fail longitudinally like that.