Besides waiting for results to become visible is there an reason a person couldn't get a 2nd Ultherapy 2 months later?

As you mentioned the full result of your ultherapy treatment may take 3-6 months. Even though I am not aware of any side effects in repeating your Ultherapy so early, it may not add any much improvement to your final outcome.  

So first of all you want to see if the first treatment did help and second you will be adding more cost. As far as the side effects etc are concerned if its done right and actually the SMAS layer was targeted second treatment will not harm but I would like to know if practices are doing this after 2 months. We usually ask our clients to wait 6 months. 

I would recommend waiting at least 3 months before your second Ultherapy treatment because it can take that long to see the beginning results in the first place.  In the mean time, I would look at other treatment options that you can do to also enhance your results from Ultherapy.