Added sugar is ok, as long as that is the only non-whole30 thing in addition to the item you're reintroducing. You should still try to avoid carraggeenan, sulfites, and msg, but sugar is not likely to cause the same kinds of reactions that legumes or dairy are likely to cause. Sugar may leave you craving more sweets, and it can affect your mood, but if you have your soy latte and find it causes gas or bloating or other digestive issues, that's probably the soy, not the sugar.
Some people do have a completely separate sugar reintroduction day and avoid it in their other reintroductions, but it can definitely be difficult to find options with no sugar.
I would not treat the fake sugars, like splenda, equal, or others, like this -- they do cause digestive issues for many people, so if you think you'll want to use them going forward, I would try to do them as separate reintroductions to get a feel for how they might affect you.