I stumbled across a useful site. Well… perhaps useful to those who do not already have a job on the mountain. It used to be the case that to check for jobs at the observatories you had to check each observatory website separately. Now you can find all of the listings in one convenient website.
The site does not identify who is assembling the information, but it does seem to be accurate, the current Keck listings are there. I found the site through a prominent link on the MKSS website. It appears to be official, but oddly enough is privately hosted at GoDaddy, not a UH or observatory server, need to see who is putting this together.