The claim was published in Shadow: Five Presidents Under the Shadow of Watergate in a chapter on Gerald Ford's presidency written after an interview with Gerald Ford. To me, that makes Woodward's claim credible.
Haig obviously doesn't feel that there was an offer made, Ford did. Whether you believe Gerald Ford or Alexander Haig is up to you, but I personally find President Ford more credible.
does allowing Judith Miller to sit in jail for months while with-holding the Armitage information enhance Woodward's credibility?