I used to work for an ISV in the finance industry. Most of our customers ran our stuff on their own servers in their own data centres, but we had direct logon to the application user account to manage the application config, do software upgrades, investigate issues, etc. A few of our customers preferred to support the software entirely themselves, we had no access and ran training courses for their support teams. I wouldn't be surprised if NSO offer a similar range of options depending on the client's budget and technical capabilities.