It will depend on the vinegar: if you're buying a jar, read the nutritional information and see what the carbohydrate per 100 is. If you are making them yourself, check the vinegar. Pickled foods are quite unpredictable- they can be very low-carb or surprisingly high, depending on the vinegar.
-I'm looking at some jars online now, and it says Van Smirren brand is 1.3g carbs per 100, so that would probably be ok for me.
Parsons brand is also 1.3g. Looks OK.
Spinnaker brand is 3.6g per 100, which isn't terrible, but it's starting to go up.
Probably best to try some then test afterwards, but they look at least ok from what I can tell.