What is local.blackjack from Netstat?
By giving an extra -n parameter to the netstat command, reveals the port number.
This reveals that blackjack correspond to the port 1025.
PROMPT&gt; netstat -anv
Active Internet connections (including servers)
Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)     rhiwat shiwat    pid   epid  state    options
tcp6       0      0  fe80::c999:dc6f:.1025  fe80::c55b:ddf6:.13569 ESTABLISHED 131072 131072    476      0 0x0102 0x00000204
tcp6       0      0  fe80::c999:dc6f:.1024  fe80::c55b:ddf6:.1024  ESTABLISHED 131072 131072    476      0 0x0102 0x00000204


In the past, port 1025 seems to have been used for something named network blackjack. Nowadays I doubt that it's still being used for this purpose.
My conclusion is that identityservicesd running on port 1024+1025 is harmless.