What in interesting idea. I have never heard of gutter heating tape as I live in an area with mild winters but I do know that warm soil helps to speed the sprouting of seeds and so heating cables for seed flats are available from greenhouse supply companies.  A raised bed is also a way to heat the soil sooner in the spring. I do think it would be safest to use heating cables designed to be buried in the soil rather than gutter heating tape. Keep growing, Marianne Binetti