Do PIs ever get outside help when writing grant applications?
The research company where I work is organized much like a soft-money university, in that we are largely organized around PIs who fund themselves and the others working on their research by writing proposals to external funding agencies.

One of the ways in which things are different, however, is that the PIs have a lot of help to draw on in writing proposals.  It's not "freelancers," because we're generally drawing on others at the company, but it's still help from outside the research group and can be extremely valuable.  In particular:


Our library staff can prepare templates and proposal checklists to make it easy to comply with formatting requirements and to ensure that the proposal writers address all of the points needed for the proposal.
We run proposals through two stages of review by people not involved in the proposal: the first is early at the "story-board" stage to make sure the narrative is coherent, the second is a week or two before submission to make sure the final proposal is really good.
Some of the company publicity folks can also be drawn upon to make nice proposal art
We used to have a professional copyeditor on staff, though I don't believe that we do any more.


These sorts of things can help a lot in producing a nice proposal, and I wish my university collaborators did this sort of thing more often themselves.  When collaborating, we often offer to organize the review stages, for example, because they really help; many university PIs, however, do "last minute" scheduling that makes it difficult to use these processes.

There is nothing to prevent a university researcher from using these sorts of resources, whether internal or external---at many universities, for example, there is a Writing Center that would likely be quite happy to help with copy-editing and the non-technical aspects of review.  Likewise, I have known professors who would review one another's proposals before they sent them out, in a less formal version of our review process.  

It just takes some organization and pre-planning to do these sorts of things... and for many of us, that is lacking without an external framework that helps to chivvy us towards remembering.