Can you use a leaf blower in the rain?

No. Leaf blowers blow air upwards of 120 MPH. Try a shop vac.

Could they? Yes in theory, I know of shop vaccum's that can suck air even though they are only connected to 150PSI. Its all in the design. See link for example...
http://www.gison.com.tw/product/P0000000149-Air-Vacuum-and-Blow-Kit.htm