In Scripture, marriage is marriage regardless of whether the ceremony took place in a chapel, the beach, or the mountains.
As for dating, I would consider how far along this person is in their divorce process. You don't want to be left out in the cold if this person decides to get back with their spouse. I would at least want evidence that there is a clear plan to dissolve the marriage.
And no, it is not adultery to date or marry someone solely because they were once divorced. That misconception is based on a misapplication of Matthew 5:32, 19:9 and other verses. It was the abuse of divorce and remarriage for selfish reasons that Jesus has a problem with, not these things per se.