Does it matter if my sales website is on a different web address or hosting?

The Arlo and LearnDash Integration plugin is purely focused on the interaction between Arlo and LearnDash, so your sales site would be separate to this.

Essentially your sales site would feed registrants into Arlo events. It is only once they are inside your Arlo platform that the plugin would recognise them and then enrol them onto specified LearnDash courses and groups. As such, there should be no issue with your sales site being on separate hosting or URL.