I have been using Oziexplorer with my Etrex for printing out maps of my tracks. The maps are very nice looking. Much more detail than the Topo maps loaded on my Oregon 550.
Is there any way to use the maps from Oziexplorer on the Oregon 550?
Not directly. You'd have to convert them using the software mentioned throughout this site.
If you want OziExplorer on a handheld, see if you can find a Triton 1500 for cheap somewhere. It is Windows CE based and can run OziExplorer CE: http://forums.gpsreview.net/viewtopic.php?t=12646
You could also convert your OziExplorer raster imagery to Garmin's custom map format for the Oregon. I have used the same source data to make maps for both platforms myself. Only problem is that the custom maps cannot cover a very large area. It depends of what you are after - I've found that 10 feet per pixel is the lowest resolution that gives acceptable results with USGS 24k topo maps. That would give you a coverage area of about 20 miles x 20 miles.