I agree, and my own reading of the poem is that it is a poem ABOUT the kind of poetry H.D. and her friends wanted to write. It's about the kind of rose this kind of poem *won't* be about. What I mean is that it refers to "rose" as a literary convention - the soft, red rose of (easy versions of) romanticism. Note that the rose in this poem isn't sweet but acrid; and there's not a mention of its color!
It's an imagist poem (I'm with various alumversers in deeming it a not stunningly successful example of such) in its own right, but it's also a
poem. A poem about the movement of which it's meant as an example.
As William Carlos Williams would write (in "Spring and All") about the metal rose - a rose of his poetry that you could cut your finger on - so H.D. here is saying: the days of squishily symbolic roses are over. This rose defies symbolic representation; it is itself. (And of course in setting up such a symbolic resistance, she takes the poem to the next level anyway.)