Technically speaking, Bada isn't an operating system per se; it's actually a platform that can utilise multiple kernels. Depending on the hardware it runs on, Bada can employ a proprietary RTOS kernel or a Linux kernel. From this perspective, merging Bada with Tizen makes some sense.
Tizen is the continuation of the failed MeeGo project from Nokia and Intel, and Samsung has been part of Tizen from day one. It makes sense they had plans with this project that went beyond a supportive statement, and this seems to be it. Apart from serving the lower-end of the market in certain areas of the world, it's pretty clear Bada+Tizen has another role to play as well.
Samsung is the largest Android vendor - and by a wide margin, too. They're also the only one posting sustained and continuous growth. Most - if not all - of this comes from Android phones (as opposed to features phones or Bada phones), making the company's mobile phone business incredibly dependant upon Google (and vice versa, but that's another matter).
As such, it makes sense to develop an in-house mobile operating system as "een stok achter de deur". If Google ever gets cocky or wants to tighten the rules too much, Samsung can simply ramp up its efforts with Bada. As such, I wouldn't be surprised to learn Samsung is also working on bringing the Dalvik VM to Bada to ensure Android application compatibility - in case it's needed.
All in all, one of the largest smartphone manufactures getting behind its operating system is a good sign - although there is always the possibility that this is a step towards actually downgrading its importance by handing over development to an open source project.
As usual, time will tell.