I've used the Garmin eTrex Legend on a 396T, 996T, 996XT and 396XT with excellent results. The requirements for GPS devices for those scanners (cables/NEMA and baud rate output) are the same for the 536. So you should expect the same results with your 536 and an eTrex Legend.
I ended up getting a 12 volt power cable with rechargeable batteries for my eTrex Legend as I was going through AA batteries way too fast.
For what its worth, I have since migrated to the Uniden GPS device for my 536. It's less obvious, thus a deterrent to thievery. Since I use GPS for solely scanning, it does the job. But if you would also use a GPS device for outdoor activities (camping, hiking, hunting) a portable device is a great choice.