The PDR article doesn't mention any link between them, but Clarke's illustrations look very influenced by Aubrey Beardsley to me. I find both interesting as examples of the kind of thing that minimalist/modernist aesthetics both destroyed and grew out of (in the sense that Beardsley and Clarke both display the Victorian horror vacui and love of ornamentation, but also experiment with huge swathes of empty space):
I saw some of his drawings for the Poe stories before I read Poe and so they always influenced my visualisation of the stories when I read them. Rich food for a teenage imagination before there was a public internet.
"Through a chink too wide comes in no wonder" - Kavanagh
If you are interested in Harry Clarke's work check out the collection of materials from his studio available on the Digital Repository of Ireland's site.
https://repository.dri.ie/catalog/9593zf44k
It includes a succinct bio.