This Fantasy Worlds chapter on Lovecraft may not be directly ERB-related, but on the other hand, Lovecraft collaborated with E. Hoffman Price on a Randolph Carter story. E. Hoffman Price collaborated with Otis Adelbert Kline on a Dr. Morgan Universe story and Kline's Doctor Morgan universe arguably is the same place as the Burroughs Universe.
Or, how about this: Randolph Carter, Lovecraft's recurring protagonist, is modeled in part on, and inspired by John Carter. A John Carter is actually named as a character from 17th century New England in the Case of Charles Dexter Ward (where Randoph Carter is also mentioned), implying that the two may be related. Burroughs John Carter is ageless, so he might well be the same John Carter from Charles Dexter Ward.