What seems to be the most successful strategy is providing a GPL product [because it is contributor friendly] and then building commercial value via services and additional features relevant to commercial users. In the case of a company like RedHat there's value is in support for all those enterprise desktop users at $150/year [more than a Windows license probably]. Other companies might extend the software with dashboards or additional features [e.g. automating backups?] that are non-free and then throwing non-free support into the mix.

My perception is that anyone who wants to install and manage an open source backup solution already has lots of options. If you're open-source, you're at least in that market segment too. For something closed source, the market is going to be smaller and swimming against the tide. Even companies with bleeding edge innovation are going open source: Michael Stonebraker's VoltDb is an example.

https://github.com/VoltDB/voltdb