I to agree with the "if you can't write it, you can't do it" school.
We have a joint pre/post award office at the University of Southern
Maine. While we gladly provide editing services to faculty that request
such, we do not get into substantive issues related to the scientific or
technical merit of the proposal. For those issues, we strongly suggest
that the faculty member work with their dean, department chair,
faculty/department peers, etc. to ensure the integrity of the proposal.
That has the added benefit of ensuring that the project is grounded in
and supported by the college and that it is in line with departmental
priorities.

As to the notion that some people can articulate their idea orally but
not in writing and therefore need the assistance, I also have some
difficulty with that. Most faculty have their students write some type
of research or term paper and there is some minimum level of expectation
as to the quality of that work. We have seen proposals from faculty that
do not meet even that level of quality or expectation. If the only way
to learn how to write (good proposals) is by writing, are we doing the
institution or the faculty any good by allowing them not to cultivate
those skills. Shouldn't we expect that they at minimum have those
skills when they are hired? Isn't this the same as providing remedial
courses to those that didn't get it in high school? I don't agree with
that either.