In fact if you're going to shoot with a rangefinder the reason is usually because you want to use a wide angle.
I use my wide angles for portraiture all the time and the 25mm is one of my favourites. There are a few secrets to getting good shots with such a wide lens. Get in close and have an interesting background. Because the field of view is so wide, it really helps if there is something going on back there. A secondary point of interest once the viewer has finished enjoying the main subject.
That's why I like to use it when shooting in a market place. There's lots of interesting things going on once your finished looking at the main subject.
This was shot on the Zeiss Ikon with the 25mm Zeiss Biogon on Ilford Delta 100. The 22x16 traditional silver print is $800.