For one thing, you can not ping from within a jail. Instead, for a connectivity test, try e.g.:
# nc -z -w 2 www.daemonforums.org 80
Also, there may be some complications due to the fact that your alias is on another subnet. Did you add a routing table entry to the host system for the 10.10.10.10 address's network? (Or is the pf nat rule really all that's needed? Not sure on that one.)