It's pretty common for LTD companies to use Allsup. Not a bad option IMO.
The LTD co has a huge financial incentive to help you. Most that have posted that have chosen to utilize the free services seem to have been happy with the services. They'll help you submit a thorough first application and will likely have you get additional documentation if needed--they may send you to a new doc/docs. You don't have to use the free service, but I would recommend doing so! You can always fire them later of course...
Many people have a combo of physical and mental disabilities, and it's highly unlikely your friend's ex would have ever found out anyway. Those that don't initially have a psych claim, often do after many years of isolation, depression, financial hardship, etc. that goes along with a severe disability.