I have evidence for one of the criteria that’s been written with letter of recommendation specs, can I add it as a letter of recommendation?
Yes if it adheres to reccomendation letter standard. The most import thing here is credentials of the person who writes it. So if you are confident of that then…
As @Mukesh_Adhvaryu said, yes, and read the article “Who cannot give you a good Letter of Recommendation?” just to be sure.