In Ord. IV d. 46 q. 1, a slightly different picture emerges. Here Scotus distinguishes, following Anselm and Aristotle (oh, wait: everything he did was to further Augustinianism. Anselm and Aristotle must just be wax noses here), two senses of justice: legal justice and particular justice. Legal justice pertains to rules laid down by a lawgiver, while particular justice, as far as I can gather, pertains to relations between individuals (I beg the readers' indulgence if I have bundled this; I generally find ethics boring and don't claim to have mastered the terminology). In this context, Scotus discusses whether justice is in God.
(Wad.-Viv. XX, 400-401):
Prima istarum, scilicet legalis, posset poni in Deo, si esset alia lex prior determinatione voluntatis suae, cui legi, et in hoc legislatori, quasi alteri voluntas sua recte concordaret; et est quidem ista lex: 'Deus est diligendus'. Sed si non debet dici lex, sive principium practicum legis, saltem est veritas practica, praecedens omnem determinationem voluntatis divinae.
Iustitia etiam illa particularis ad se, quasi ad alterum, est in ipso, quia voluntas sua determinatur per rectitudinem ad volendum illud quod decet suam bonitatem; et haec est quasi redditio debiti sibi ipsi, id est, suae bonitati, tanquam alteri, si tamen posset dici particularis, quia aliquo modo est universalis, sciliet virtualiter.
Et illa duo membra, scilicet iustitia legalis et particularis ad se quasi ad alterum, in Deo quasi idem sunt, quia rectitudo voluntatis divinae respectu suae bonitatis.
Translation to follow.
In the end, I think we can derive the following point: this passage may not help us determine to what degree Scotus was a voluntarist with respect to the human will, but certainly in the case of the divine will God will always will in accordance with his goodness; and how does the will acquire this goodness as a material for willing? Well, it would have to be supplied by the divine intellect. So the passage is another example of Scotus' view of God as a most ordered willer, whether or not one thinks his account of the mechanics involved (formalitities of intellect and will acting as co-causes of volitional acts) works.