I'm afraid that the bottom line is this:
1) Orchestrators and Engineers get paid. If the composer does really well out of the film, it is extremely unlikely that they will pass on a bonus. Do orchestrators get a share of the Royalties? Not in my experience.
2) Just because an orchestrator has worked for a composer before, it doesn't mean that they will be asked again. I was bumped off a film earlier this year simply because the Producers were unfamiliar with the Director's choice of composer and insisted on a team that had worked on one of "their" films before. I had worked for this composer for around 4 years, earning him 2 BAFTA's in the process.
So as I said in point 1), orchestrators get paid. If you can't afford an orchestrator, then do it yourself, or use samples. Why should the film company get something they haven't paid for anyway?
DG