I think Roth would have wanted Ola to keep an eye on Michael's movements, and to report on if/when/where the money Michael was supposed to be bringing arrived. Michael would have allowed Ola to do this because he wanted Roth to think he still trusted him and because he wanted Roth to know that the money had still not arrived. Once Michael arrived in Cuba he was relatively safe from being assasinated by Roth until after the investor meeting was done and the deal was in place, because killing Michael before that would have made all the other investors very, very nervous.