As has been pointed out, 'Scenes from Comus' does indeed reference a masque (and also references Hugh Wood's music based on 'Comus') and does so in a way that could be said to be equivocal about the power relations involved in presenting a masque to a powerful patron. There's a good discussion of this in Signals magazine. As to whether a single line should be taken out of context, the answer is, probably not, so here's the whole stanza:
With splintering noises the ancient tannoy
celebrates more delay like a bequest
or benefaction long overdue.
An ordinary day, one more rehearsal.
Ducking and weaving, the last flight goes in,
the voice of reason maddens with its fear;
voices of prophesy assail the dead.
In the previous two or three stanzas, 'I' and 'me' is used, and as the above seems to be set in an airport (or at least a metaphorical one), we can assume it's the poet-narrator persona who is speaking here, and in the context, I think we can say that the line 'the voice of reason...' does seem to be ambivalent about reason itself (or at least that's a possible interpretation). Much of this long poem is didactic in style, and the poet-narrator makes what appears to be personal statements of opinion about things, including (as in much of Hill's late poetry) old-age:
implausible, credible muse
whom I assuage by night
Where are we sans our lovers, you name the place?
The place itself if common; I have been here many times and enough.
So, in this context, the line about being a 'portal for the heirarchies' can reasonably be interpreted as being statement about what the poet-narrator would like to be. Hill is Professor Emeritus of Literature and Religion, and, of course, religion is all about hierarchies.