The danger of using inkjet paper in a laser printer is the heating process that fuses the powder to the paper could melt/damage the paper, spread it around the insides of your laser printer, and ruin it. Laser photo paper is designed for the high heat of a fuser.
Using laser paper on an inkjet will probably just cause the ink to bleed and smear into an unattractive image, as the chemicals needed to prevent the ink from spreading and smudging aren't present. It will likely look like passing plain copier paper through the inkjet printer.
They likely have a different feel/texture/gloss that an experienced paper person could tell by looking/feeling, but I couldn't tell you what that is. Maybe go to Staples/OfficeMax/etc and see if there's an obvious difference (if they carry both). Or just toss it to be safe. Your situation sounds the the one where damage could occur, and I suspect inkjet paper is much more prevalent than laser photo paper, so in lieu of further data, it could be quite risky/damaging.