Dennis Morgan is a well known songwriter who has written with Rob and Simon quite a bit, and continues to write with Simon. He is from Nashville, If you can help out with any information on Dennis please contact me.
 

Dennis Morgan released a cd in 1996 titled Attic Chronicles Vol. 1, where he recorded songs that he has written for other people, here is a track listing:
1.   Sweet Emmylou (w/Harlan Howard--about his crush on Ms. Harris)
2.   Free Man
3.   Roll On Mississippi
4.   I Can't Get Enough Of You (w/Willie Dixon shortly before Willie died)
5.   I Was Country When Country Wasn't Cool
6.   Airport Hotel (w/ Roger McGuinn who did record their collaboration Suddenly Blue)
7.   I Owe You One (Another w/ Harlan Howard)
8.   The Older Woman (w/Donovan at his house in Ireland)
9.   My Heart Can't Tell You No (w/Simon Climie--different from the version Rod Stewart recorded)
10.  Tennessee Moon (w/ Neil Diamond, in Neil's Nashville phase)
11.   Interlude...
12.  Blessing In Disguise
13.  When I Get Through All This (w/ Gary Busey shortly after Gary's accident)
14.  Chet (Paean to Chet Atkins written by Dennis years ago when he was starting out--Chet heard
      about it and  offered to record him at his studio. He and Chet trade a few licks on this.)
15.  The Big Ole Platinum Record (w/Shel Silverstein, with whom Dennis often wrote. RIP, Shel)
 

According to the Midwest Underground the cd is still avaible, contact them for more information.