There's no issue with using a Roku device in a business environment. You don't *subscribe" to Roku. Roku themselves offer no media other than The Roku Channel, and that's merely content they've licensed from the content owners. The issue because the content you're displaying. Playing music from Pandora or Spotify would need to have a user account that permits use in a business setting, which I believe both offer. If you're streaming media (movies or music) from a local server, again you have potential copyright issues with the content owners. Remember that buying a movie or music on a disc or via download doesn't actually give you ownership of the content. You get the legal right to play the media for personal use. Any business use technically requires a different license.
Of course, one might question if it's something that would ever be discovered by the content owners, and open you to legal liability. Depending on the media you're playing and how you're streaming it (again using Pandora or Spotify as an example), the odds of them discovering you're using a personal account in a business setting is really slim.
You mentioned businesses creating their own channel for Roku devices. That option no longer exists, as Roku has significantly clamped down on developers creating and publishing private channels. Now they are both time limited and can only provide them to a limited number of users. They are only to be used to test new channel releases, not for continual use.
Dan
Roku Community Streaming Expert
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