Thanks Hko and pixellany
A couple of links for anyone netsearching this issue.
There's some discussion of zenity and focus at https://bugs.launchpad.net/zenity/+bug/272083
including Hko's suggested workaround and a version of zenity with a --focus option (but it's probably both "on top" and focus).
Zenity enhancement requests are listed at http://live.gnome.org/Zenity
after clicking "More information". It includes an "Always on top" enhancement request but nothing about focus.
I submitted an enhancement request for a command line option not to grab focus.
If I get kdialog's nograb option to work, I'll post back.