Every employer is different, the list would be nearly endless, my airline doesn't have qualms about it as long as the pilot or engineer wishing to do so gets an ok from management (it has happened before).
That being said, there is a terrible attitude amongst companies and HR groups these days that suggests it's ok to hire people with less than stellar flying ability, so long as they have a good "personality" and can "get along with others" etc. etc. etc. I'm not trying to suggest "good sticks" should go around being
. In my opinion the #1 driving factor as to whether or not to hire somebody is their abilities in an aircraft, on both the flying side and the technical side (systems). How they comb their hair, talk, who recommended them or how nice they are should be near the bottom of the list, not the top.
Furthermore, GOMs an SOPs will not and never have covered every single possible situation that may arise. Yet most flight crew members are afraid of doing anything (or unable to do anything) that falls outside of what is referred to as "standard".