I think it can work but I also think it can work against you by making the domain rather long. Usually it's best if you're just sticking to (keyword) online.com, or (branding) online.com, rather than the combination.If you're able to work with an established brand, like Skywarn, skywarnonline works - because it's showing the branding+online. If you're trying to create a new branding, perhaps go for keyword+branding rather than keyword+branding+online.