what does the "symapi server" icon mean under the ECC agents ?

The icon means that at some point that host was discovered via symapi server. Hosts like this will pop into the tree if you perform a proxy host or database discovery using the Common Mapping Agent (CMA). Or if you try to discover a Symmetrix array via proxy as well. The icon will not go away unless you delete the host which might not be an option in your setup. There is no harm in keeping the icon there. There is more detailed information about proxy based discovery for the CMA and Symmetrix agents in the console online help.