No, you absolutely can't delete those. Indexes is an integral part of how SmartEvent and our logs mechanism works.
If you will delete indexes you won't be able to use SmartView and the logs correlating with the indexes wouldn't show on the logs view.
Every server that we use for logs/SmartEvent will be out of space eventually but for that we have cleaning mechanism. We have daily and emergency - for daily you can define how many days of indexes to save and how many more days of saving logs. With emergency you can define threshold of minimum space on disk and when it gets to the threshold it delete the old ones.
Kind regards, Amir Senn