The /etc/services is simply a mapping by which various different programs use the getservbyname and getservbyport calls to map between the ports and names various services use.

You can have multiple lines but exactly what happens when you do so will depend on the implementation of getservbyname and getservbyport. On Solaris the first matching entry in the /etc/services file is used so multiple entries dont make much sense other than to provide a human readable record.