Scopus is the well-known database while the SCImago Journal Rank (SJR) indicator is developed to show the visibility of the journals contained in the Scopus database. Therefore, All journals included in SJR are indexed in Scopus but not vice versa.
No. SCIMango is a collection of tools, metrics that work on the Scopus database. The well-know metric to measure in Scopus is CiteScore, but SCIMango uses another score SJR. So, they are same, only different for ranking. Journals ranking in Scopus uses SJR other than CiteScore. This is equivalent to JCR in Web of Science database.