I did install it afterwards (I copy and pasted the install lines and forgot to run the make install because I was having problems compiling it because of limited VPS resources prior to that). I did find some instructions that said to run update.php if you install jailkit afterwards so I did so.
I installed the version located here: http://olivier.sessink.nl/jailkit/jailkit-2.5.tar.gz
as set fourth in the instructions.
I'm just starting out so it wouldn't be hard to do a complete re-install if you think it's necessary.