Ideally? Never. You risk component break down by re-running the board over the wave machine. In a perfect world, your wave operator would make adjustments after one run, and you'd run another panel over the wave to judge the effectiveness of the adjustments. Besides, the solder presence from the first run may skew your results in the second run.
Functionally, of course, we've done this with regular thru-hole assemblies. I don't glue/wave anything currently; but have in the past. And, of course, we've had to re-run a previously waved board. I'd strongly recommend making it an extreme exception, however.
As to the components...what is your fear? Losing the Melf's over the wave, or their tolerance to the process? Spec sheets will give you the info related to their tolerance to the process. I'm not certain what you'd run into re: losing the parts, though...my memory is hazy as to what I've experienced in the past related to this. I would, initially, expect that you wouldn't lose parts...the glue shouldn't break down, and you've got surface tension on your side.
cheers, ..rob
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