What are these slowly pulsing white dots on my scanner?

I just answered this as part of my answer here, but I'll rework it for you, since your question is sufficiently different than the linked one.

When you use the Analysis Visor, it will show three things:

• Green Dots

These indicate creatures that you have already scanned.

• Red Dots

These indicate creatures that you have not yet scanned.

• White Dots

From my experience with the game so far, the white dots do indeed appear to be creatures. They only stay for a few seconds, presumably so that creature finding isn't an easy task, since the reward for 100% is so high. The game does not seem to be intuitive enough to tell you if you (from a distance) if you have scanned them or not. However, the closer you get to a dot, it will turn green or red depending on what you've done for that species.