First of all: FMS 5.5 on Linux was only certified on Red Hat so I wouldn't expect it to run well on CentOS.
Other than that; it sounds like a permissions issue. Do you have any snapshots of the old setup to check the permissions against?
Discovered /tmp was 755
[root@filemaker /]# chmod 1777 tmp
[root@filemaker /]# /etc/init.d/fmserverd start
Starting fmserverd: [ OK ]