Success = true. The call to the service succeeded and it ran like it should, the IP was ok etc.
<servers/> means no servers were returned, so no servers on this IP are listed on the masterserver.
This is how it shows if it returns any servers:
<success>true</success>
<servers>
<server>
<addr><IP_HERE>:27018</addr>
<gmsindex>65534</gmsindex>
<appid>10</appid>
<gamedir>cstrike</gamedir>
<region>255</region>
<secure>true</secure>
<lan>false</lan>
<gameport>27018</gameport>
<specport>0</specport>
</server>
</servers>