Found out today, Yes, using a laser sight for bow fishing is legal.

It falls under section 3 CSR 10-6.410(12)"As an aid to fishing methods, an artificial
light may be used only above the water
surface, except that underwater lights may be
used to attract fish while fishing by pole and
line and when bowfishing on impoundments
as authorized by 3 CSR 10-6.550. "

I hope this helps,

Andrew Branson
Fisheries Programs Specialist
Missouri Department of Conservation

Thanks Andrew