Perl 6, 77 bytes
{my \z=[+^] @_;elems([""])eq(sum z.polymod(sum(elems([""]),elems([""]))xx*))} This is equivalent to
{my \z=[+^] @_;1 eq([+] z.polymod(2 xx*))} 1 was rewritten as elems([""]). 2 was rewritten as sum(elems([""]),elems([""])); elems(["",""]) might seem to work but elems([""-""]) is also valid and seems to hang the tester.