High availaibility for highly transactional applications

Using the same VIP at your backup DC would likely require some kind of supporting network routing change to send requests there vice your active DC. If you used a different VIP at your secondary DC and setup load balancing to always prefer the VIP at your primary DC unless it was down, and then and only then to send traffic to your backup DC, that may be cleaner.

Of course, you're probably going to encounter at least a little disruption in service between the time your server goes down and the time the BIG IP marks it down and starts sending traffic to the backup DC. You can better control this through the interval and timeout values on monitor you set.