I have /vicepa (about 500MB) and /vicepb (about 500MB) on different
 servers, both are Ext3, and I would like to group them to expand the
 space.

 I edit /vice/db/vicetab on SCM and add a line for /vicepb, and after I
 restarting the server:

 scmserver	/vicepa		ftree		width=256,depth=3
 non-scmserver	/vicepb		ftree		width=256,depth=3
 
You did not explain how your volumes are set up.   Volumes are in server
groups, which define the set of servers the data is stored on.  If
vicepa is full and vicepb on another box is not, you probably have a
singly replicated volume on scmserver.  You can't use space on
non-scmserver to augment this.  You can make a new volume in the
non-scmserver server group and mount it.