ocsp.apple.com also has an IPv6 address. Firefox connects to it even with 0.0.0.0 in the hosts file and a flushed cache (you need to also clear firefox's internal cache if you're testing with it), so I'd assume that trustd could connect to the ocsp site as well. I don't think this will work without ensuring there is no IPv6 traffic on your network, or otherwise dumping both IPv4 and v6 packets to ocsp.apple.com.

Disable IPv6: sudo networksetup -setv6off Wi-Fi (where Wi-Fi is the name of the network service)