You will find Severus routinely referred to as a monophysite in Byzantine Orthodox literature.
Examples from the hymns:
O mindless and vain Severus, tell us: is the Word, the Son of the Father of lights, a single essence, commingled, unoriginate? For if thou sayest so, thou dost postulate a different essence; for flesh and the Word are not a single essence, but are two, O wretched one!
The six hundred and thirty pious men, having cast down the deception of Eutyches and the heresy of Severus, attained unto this hymn: We preach Christ in two natures, walking according to the pronouncement of the blessed Cyril!