When I first created my EE profile I was not aware of what does and does not give points. So I listed all my spouse's work experience. Then I got ITA, went through the application process...and of course each of his work experiences was listed and a reference letter was required. But he wouldn't be able to get reference letters for most of these (employer doesn't exist anymore etc.). So I checked...CIC didn't award any points for his experience...so at the ITA stage I just changed to "No" when it asked about whether spouse has any work experience. All the fields where one would have had to add reference letters also disappeared with that. Since we were not claiming any points for his work experience, that's totally fine, no explanation letter needed, as long as you are not claiming points for it, CIC does not care. So in short: if you are not claiming points for your spouse's work experience, then there is no need to mention it or provide reference letters.