I gave a recommendation that for CDC to use Snapshot isolation due to two reason.

1. To make sure that there is no blocking caused when trying to get the LSN.

2. To make sure that you get the right LSN.

On a busy OLTP server, you are going to have high number of data changes and that means that the Max LSN will be changing at a very rapid rate. You want to make sure that the MAX LSN is the same through out the query you are using to retrieve the changes.

But it all depends on how you are retrieving the changes. There fore it is just a recommendation. It is not a must. I hope I was able to answer that question.