It depends on what specialty grains you are using. Some have enzymes, others do not. Malted oats would provide enzymes, for instance, but would also have a somewhat different flavor to the unmalted oats that are more commonly used.
Generally, though, some amount of base malt is a good idea. Not just for the enzymes, but also for the barley husks - without those, you're going to end up with a sticky mess of porridge that won't be easy to sparge!
Can we see your recipe? I would start with at least as much base malt as you have oats, probably 2 row or maybe 6 row, but it really depends on what else is in there.