James, I had the same issue – very frustrating not finding detailed “svn merge” info; however, in my google searches I found this posting: http://svn.haxx.se/users/archive-2008-06/0813.shtml
It indicates that the “svn merge” status letters are identical to the “svn update” status letters, which are actually documented. From the “svn help update” command:
For each updated item a line will start with a character reporting the
action taken. These characters have the following meaning:
A Added
D Deleted
U Updated
C Conflict
G Merged
A character in the first column signifies an update to the actual file,
while updates to the file’s properties are shown in the second column.
A ‘B’ in the third column signifies that the lock for the file has
been broken or stolen.