While it can be done, it's going to sound terrible (or at least not sound like the amp is supposed to sound). So much of what makes up an electric guitar sound is the full amp and speaker. Just taking a line from the effects loop is not going to sound like the amp through a speaker. Distortions are going to sound very fizzy and unpleasant. Clean sounds might be OK, you'd have to try it and find out.
What you are talking about doing is similar to if you take a guitar into a distortion pedal and straight into a recording interface. By removing some of the key components (mainly the amp preamp/power amp and speaker), you are drastically changing the sound.
If you want to try to record the amp without using a mic, you will want to get a speaker simulator. There are more and more of these on the market nowadays, I think Pete Thorn recently reviewed a speaker simulator pedal which you plug your amp into. This will allow you to skip the mics and still get the correct type of sound from your amp.