Musa was indeed one of the 12 Imams and is revered by Shiite Muslims, but does that make him a saint? In the generic sense, if there is one, I guess he is a revered as a saint, but as explained here, it’s not quite the same in Islam as it is in Christianity.

In the Protestant tradition, anyone who displays the qualities of a good follower of the faith can be considered a saint. While it’s fine to consider one’s grandmother a saint, in that generic sense, one would have difficulty tagging John Calvin or John Knox with the title.

In the same sense it is wrong to tag a Muslim Imam with the term in a journalistic setting because there are more accurate ways to refer to him and it places him in a category that doesn’t even officially exist in Islam. ~Daniel Pulliam, GetReligion

I suppose it is a fair point that it could be misleading for a Western audience when someone refers to one of the Imams as a saint, since this carries certain connotations in a Christian context that could create confusion about the figure being so described. But is it really an inaccurate or inappropriate term to use? Is it wrong to use the term saint when speaking of Islamic holy figures? I don’t think so, not least because the word itself simply means “holy one,” and there are numerous examples in Islam of venerating and praying to their holy figures to honour them and ask for intercession.

In modern literature on Sufism, it is commonplace for scholars to refer to fakirs, wonderworking mendicants, as saints and their graves as shrines. To be called wali Allah (friend of God) is to be acknowledged as just such a saint–this is a well-known popular title of Caliph Ali himself. Certainly the veneration their graves receive bears striking similarities to practises at the shrines of saints. This is an aspect of Islamic popular religion that may not always have express support in Islamic scripture or tradition, but which takes place nonetheless. In the centuries after his death, the mystic and “martyr” al-Hallaj was venerated in such a fashion because he was respected and honoured for his piety in spite of being executed in 922 for the blasphemous utterance, Ana al Haqq (I am the Truth). (It is of passing interest that this statement, so similar to that of the Lord in Jn. 14:6, led some early enthusiastic scholars of medieval Islam to suppose that he was some kind of oddball heretical mystic Christian, but this seems entirely untenable.) Further, the famous mystic of the 13th century, Ibn Arabi, got himself into some trouble by stressing the superiority of sainthood over that of prophethood; in any case, the distinct concept and category of Muslim holy figures comparable to those whom we would normally call saints was a well-established one in medieval Islamic thought. As the Wikipedia article Mr. Pulliam cited itself says of Muslim saints:

Saints are believed to have a power of intercession with God (Allah), and thus the ability to perform miracles and to give power or blessings known as baraka.

If this is true among Sunnis, how much more true is it among the Shia, whom takfir Sunnis routinely castigate for praying to men (i.e., the Imams)? Structurally, Shia Muslims treat the Imams as spiritual intercessors and holy figures in a way similar to, albeit not the same as, Christian venerations of saints. They do this in recognition of what they believe to be the special spiritual status and perfection of the Imams, whom they venerate in anticipation of the coming of the Mahdi. This is particularly true of Iranian Twelver Shi’ism, the branch to which Iraqi Shia belong.