Apple - nslookup works with /etc/resolv.conf, ping and ssh don't

I had the same problem. The solution I used was to create an /etc/resolver directory. Inside that directory, create a file named for each domain you wish to resolve for. Inside each file there should be two lines

nameserver 10.0.100.2
domain  home.cainmanor.com

The file above would be named /etc/resolver/home. It may need to be named home.cainmanor.com, but I can't test it right now.

Good luck!

Well, did you read the comments at the top of /etc/resolv.conf?

# Mac OS X Notice
#
# This file is not used by the host name and address resolution
# or the DNS query routing mechanisms used by most processes on
# this Mac OS X system.

The correct solution is to add the search domains via the Network panel in System Preferences as described here.