That depends. To be absolutely safe, you should, however, a good tune is some big bucks.
Depending on how much juice you plan to run, you should keep your timing at stock or retard your timing. For a 100 shot, I would keep stock (10) or retard to 8. With the diablo, you won't be able to do this. The diablo allows you some adjustment, but you can only retard your timing 10% of the 4% advance. Which means if your diablo tune has you at 14 degrees and your retard it 10%, you will be only at 13.6 degrees. The diablo allows only very fine adjustments. To be sure, check with diablo.
With my SCT, I can store upto 4 programs. I have a stock tune, a 93 octane tune, an 87 octane tune, and I am adding a nitrous tune for my setup. With the SCT nitrous tune, my timing will be retarded and my fuel richened a tad.
By all means, if you are gonna run the nitrous, put the stock tune back on the car. That's what I would do. And, keep your spray conservative untill you can at least verify your a/f.
All you'll need is a timing adjuster to retard timing 1 degree for a 100 shot. 2 degrees for more.
Edit: Didn't see that you had a Diablo Predator. Just use the stock tune and knock the timing back a full degree and you'll be golden. Do not use their performance tune, make sure to use the stock tune.
You'll need colder spark plugs, but not a tune. You can adjust the a/f using the fuel jet with a wet kit, no need for a tune. If you spray a 75 shot or lower, you don't even need to bump back timing, just get the plugs (Autolite 103s are good).
If you do get nitrous (I strongly recommend it) get a Nitrous Express wet kit.