It's a good idea to commit the cassettes because this way they can be reused by the CI server making the build faster. But Usually while rebasing master we get many conflicts on the cassettes the reason for that is because when a request changes or the cassettes expires it is re-recorded locally and sometime this same cassettes was already pushed by an other developer, the fix for this problem is explained bellow:
git checkout your_branch
git pull --rebase origin master
git checkout --ours spec/cassettes
git add spec/cassettes
git rebase --continue
Remember to fix any other can conflict normally and use steps above whenever you get conflicts on your cassettes.