active/active LTM deployment on different subnet

The high level answer to your question is Yes, but the devil is in the details.

 

 

The GTM is to Datacenter Load Balancing what the LTM is to Local Load Balancing. The GTM can do Active / Active Load Balancing based on whatever criteria you provide like Geographical Location.

 

 

However, the VIP's are not "moved", the traffic is redirected at the GTM Level based on Health Checks that the GTM does on the Local Datacenter LTM's (much the same way that an LTM marks servers available or unavailable in a Pool).

 

 

I am seriously over simplifying the setup description, but it this is something you are interested in then you will need to do additional research. Keep in mind that the F5's / BigIP's do not do data concurrency for your applications (you have to do that on the back end) and that alone might kill the concept of Active / Active.