Answer to re-posted question above (originally found at the blog post, http://ez.analog.com/community/rf/blog/2014/03/15/adl5391-outputs-while-disabled):
Hi Victor,
The output impedance is about 350 Ohms at low frequencies when the part is disable. Please see the attached VNA data. Outputs goes 2.5V on a 5V supply while being disable.
Thanks,
Joel