I am not a rigger and really am not qualified to be giving advice, but it seems to me that you should be able to use an industrial chainfall to hoist and lower the truss, but you would then need to provide approved and properly installed rigging to suspend the truss during the show. In other words, the hoist is used ONLY for moving the truss, and is NOT used for static suspension.
The chainfall should not be under load except during hoisting/lowering, and even then you need to take appropriate safety measures: controlling access to the area, using spotters, PPE, etc. Another thing to keep in mind is that the hooks on an industrial chainfall are not locking; the load could slip out and drop in the event of unplanned or poorly-planned movement.
That approved and properly installed static rigging may cost as much or more than an approved and properly operated hoist.