580EX II with 70-200mm f/4L

Would a 580EX speedlite pair well with a 70-200mm f/4L (non-IS) on a Rebel XTi for portrait work? The flash coverage of the speedlite is from 24-105mm but the 70-200mm on a crop body is pretty much all beyond that focal range.

No problem at all. You can even shoot it all at 24mm. Wide is good. It covers everything that is longer, but it will waste light. (and batteries).

That is why it zooms out to 105mm to try and match the length of the lens. With your 70-200, the flash head will auto-zoom between 70-105 only, but 105 will light up the whole scene plus more. (provided it is on the flash and not off camera)

Here is one w/ the 580 EXII, xti, and the 70-200 f/4 non-IS.

That shouldn't be a coverage problem. Keep in mind that shooting from long distance with a long lens and on camera flash, the lighting will be very flat, and there's a greater chance to get red eyes.

And depending on the ISO and aperture, you may not have the shooting distance either.

The 580 has a Guide Number of 58 meters with ISO 100. That's good for about 14 meters or 43 feet at f/4. At f/8 that would drop about 7 meters or 22 feet.