I don't really see why "Lovecraft" or "Armitage" would be a theme player. For me, the character to express that would be Randolph (Carter),* the dreamer par excellence who obtains full immersion in the Dreamlands. I'd see Armitage** (the librarian) as someone who tries to exploit obscure and undervalued cards, building decks around them.
I think the campaign-oriented co-op suggests some additional types, not focused as much on deck priorities as on play patterns:
(Richard Upton) Pickman***: Likes to re-play and fine-tune earlier scenarios.
(Henry) Akeley****: Always eager to get beyond the scenarios in hand.
Asenath (Waite)*****: Has a irrepressible tendency to coach other players, trying to "possess" their characters, as it were.
* "The Silver Key," etc.
** "The Dunwich Horror" and others
*** "Pickman's Model"
**** "The Whisperer in Darkness"
***** "The Thing on the Doorstep"