pros and cons of submitting a conference paper in first round vs second round
The conference's important dates precisely mention both dates, namely the first and the second submission rounds. Although I understand your worries, I do not explicitly see on the CfP that the two overlap.
So I would suggest you to move as you planned. But! In any case, since those sensitive matters are not well defined, you can easily send an e-mail to the respective organizing committee/program chairs with your question. Thats what I would do if I were you.