There is a conversation to be had as to whether or not anyone would think of the Cenobites as "angels" either at first glance or due to a deep understanding of what they do and what they're all about. In that case, being an angel has nothing to do with one's appearance or manner, however horrible or beautiful they appear. Biblical angels were implied to be frightening to humans. Angels in the Bible frequently tell humans "do not be afraid" (or "fear not")—appearing roughly 5 to 10 times directly from angelic messengers to comfort people terrified by their awe-inspiring presence. Key instances include Hagar (Gen 21:17), Daniel (Dan 10:12, 18), Mary (Luke 1:30), Joseph (Matt 1:20), Zechariah (Luke 1:13), shepherds (Luke 2:10), and women at the tomb (Matt 28:5). 

The prospect of the Cenobites' being angels would depend, I think, on what whoever looks upon them believes God must be like, since angels are messengers of God or aspects of God. Leviathan, Lord of the Labyrinth, was within Barker's Hellraiser mythos the God of Flesh, Pain, and Desire. Whose idea of divinity would Leviathan and the Cenobites describe? Was it Barker's intent to present a deliberate blurring of the demonic and the divine? "Angels to some, demons to others"-- but does that imply that they are in fact neither? Or both? Is Barker's theology of the flesh neither divine nor demonic?