Hi,
Now there I'm afraid you have me.
I have never seen it - but if it is good quality tape designed for high temperature environments then it should be ok.
Hopefully someone with direct experience of it can answer your question.
But as an aside make sure you insulate the cut ends of the flexwatt with electrical tape before atattching the foil tape as it is conductive in all likelyhood.
Safety first.
dr del