>>288634947
I don't see any demos with more than one of them, but I don't see any glaring reason they couldn't work as trackers. Their paper claims that there isn't any limit to the number the number of trackers that can be used simultaneously, so I don't see 3 of them being an issue. It also says the initial cost to throw one together was $75 though, so I don't really think it makes sense to try making them just to save money. If you just want a project though, it might be fun.
I think they were designed for SteamVR 1.0 base stations, so you'd have to use those instead of 2.0 ones, and you might have to write your own SteamVR driver for them since it doesn't look like they actually made one.