Yariv,
Let me try to answer your question on whether does LabView takes over VB-written codes or vice versa. Now, from my experience with this E5071B Network Analyzer using LabView, Visual Basic and VBA macros, I believe any of these program can still take over the function on the ENA at any period of time (even if you have several of these running at the same instance). Actually, when I have a program controlling a ENA, I can still override the original program's setting with another program and provide a new set of commands and/or settings (but I am sure no one in the right mind would attempt to do this as it will affect the test results.)
My first concern is whether "other" programs can immediately detect the change or command that was directed to the ENA. Earlier on, I had several bad experience where the communication channel between my tester and ENA is dropped unexpectedly, resulting in a loss of control of the ENA. I am still unable to detect and resolve the cause of concern.
Continuing further, I don't think I am in position to help you with your second question, as my search around NI's website on this ENA seems rather limited. If I have any leads, I will post it here then.
On the sideline, if you are interested in running VBA macros directly on the ENAs, do check out Agilent's website as there are a list of Agilent-written codes for some of the general functions. On top of that, you may be interested in evaluating Agilent's IntuiLink. I doesn't personally use it in my line of work, but it seems to provide most of ENA's functionality through Microsoft Word and Excel.
Have you tried to direct your questions to Agilent Japan? That's where the support and development team are. If not, you can compile a list of questions, and I can assist you to contact Agilent Japan, as I am currently attached with Agilent Malaysia. It shouldn't be much of a hassle.
Cheers,
JL Chew