The LE will work fine in an effects loop for delay/reverb/modulation, but ONLY if the loop is a series loop, or with a parallel loop where you can divert 100% of the signal through the loop (effectively making it a series loop).
This is because all these types of unit have AD/DA (analog/digital-Digital analog converters) in them. THese converters slow the signal by a few milliseconds. So even with no effects on, your signal will be slowed by a few milliseconds. If the whole signal goes through the loop and then on to your power amp, then all will be fine, as you brain is not able to perceive the tiny delay in your signal.
However, in a parallel loop you would be merging the "dry" (unprocessed) signal back with with your processed (slowed) signal through the Tonelab. When you do this you get unpleasant phasing-type effects.
It's not dangerous though. So, if you are not sure what sort of FX loop your amp will have, just give it a go. The presence or absence of wierd phasing will let you know what type of loop you have.
I have done this in the past with a Tonelab SE. It worked fine with a series loop. However, I will say that, in general, individual Boss pedals would give much better quality effects. I was very impressed with the Tonelab's reverb though. It is also very interesting to play around with adding cab sims in the FX loop of a tube amp - some great, and unusual sounds can be had this way.
