run off battery when cruising?

The Escape Hybrid will use the gas engine for motive power generally when running over 25 to 30 mph. If you should need additional power when passing, etc, at highway speeds, the electric motor can kick in to give additional power.
You should expect to get 30+ mpg running on the gas engine at highway speeds. The big savings come when you are in slower, stop and go traffic when you can operate on battery power alone (up to 38 mpg.)
If you are coming from a vehicle that gets 20 mpg or less on the road and 15 or less in town, like most SUV's, the Escape Hybrid may fill the need nicely.

The Prius can run exclusively on electric power up to 42 mph. After that the gas engine has to turn simply to keep the RPM of the electric motor from ripping it apart. However, it is possible for the Prius to turn the gas engine without supplying fuel or spark, so given the right situation (usually downhill) it is possible to cruise without gas power.

The Escape's hybrid system is essentially similar to the Prius' (especially the 2001-2003 Prius) so I'd expect it works similarly.

Honda's system is completely different, the electric motor and gas engine are on a common crankshaft so when one turns, the other must also turn. Also the electric motor on the Honda is designed only to be able to start the gas engine and or provide a brief boost to the gas engine. It can't power the car by itself.