hey i think u got to check the manual for your e500. i think it can be used. but its safer to read up the manual first !
here are a direct copy and paste from the oly e300 manual
Using commercially available flashes
The amount of light emitted cannot be adjusted on commercially available flashes
except for those specified. A small versatile flash can be synchronized with the
camera at a shutter speed of 1/180 sec. or less, whereas a large flash (such as a
studio flash) can be synchronized at 1/125 sec. or less. For details on nonspecified
commercial flashes, refer to the next page.
1 Remove the hot shoe cover to connect
the flash unit to the camera.
2 Set the exposure mode to M mode,
then set the aperture value and
shutter speed.
~Manual shooting (P. 49)
● A slower shutter speed may produce blurred
images.
3 Turn on the flash.
● Be sure to turn on the flash after attaching
the flash unit to the camera.
4 Set the flash control mode on the
flash to AUTO. Also set the ISO
sensitivity and aperture value on the
flash to match the cameras settings.
● Refer to the manual for the flash to set its
flash control mode.
Flash shooting
● The cameras flash mode except 2nd curtain will have no effect on the nonspecified
commercial flashes.
● The flash fires each time the shutter is released. When you do not need to
use the flash, turn off the flashs power.
● Check beforehand that the flash you are using is synchrorized with the
camera.
Note
Non-specified commercial flashes
Before selecting a non-specified commercial flash, be sure to read the following
information carefully to determine whether or not it can be used with this camera.
(1) Exposures when using a flash require that adjustments be made on the flash.
If a flash is used in the auto mode, match it with the F value and ISO
sensitivity settings on the camera.
(2) Even if the auto F value and ISO sensitivity of the flash are set to the same
conditions as those on the camera, the correct exposure may not obtained
depending on the shooting conditions. In such a case, adjust the auto F value
or ISO on the flash or calculate the distance in the manual mode. (Exposure
compensation on the camera cannot be used when shooting with the flash.)
(3) Use a flash with an illumination angle that matches the focal length of the
lens. The focal length of the lens for 35 mm film is approximately twice as
long as the focal length of the lenses designed for this camera.
(4) Do not use a flash unit or other accessory TTL flash that has additional
communications functions other than the specified flashes, since it may
not only fail to function normally, but may also cause damage to the
cameras circuitry.