Can I use 26" electric hub wheels on a vintage road bike?
It's quite unlikely. The axle length (hub spacing) will probably be rather different. 

Here's a list of axle lengths. The same page also discusses how you might get away with it on a steel frame with quite a lot of effort. 

Then you get onto the wheel building, which isn't easy and had to be good for electric wheels with their greater stresses. The 26" wheels wouldn't reach your brakes, so I assumed you use the hub motor and your existing rims with new spokes.