I sell lumber and hardwood flooring. You couldn't have done hardwood any thinner than 5/8", and even at 5/8" you risk snapping the groove. Most floors are 3/4". Liquid Nails is perfect for gluing down flooring, but let me run this question past my boss in the morning. After he scoffs and laughs at me for mentioning engineered flooring, I'll make him answer me, and get back to you. Usually, installers will glue and blind nail them on the tongue. I take it there is no radiant heat underneath? No pipes to worry about?
With wood, you want the substrate and the floorboards to be no more than 10% different in moisture content, if the back of the engineered floor is wood too (even plywood) let them acclimate in the room first, which by now is probably already done. The key to gluing is the substrate has to be CLEAN, CLEAN, CLEAN! Don't let any glue come up between, and don't let dust and debris get into the glue, or underneath.
At the risk of sounding like an ad, this is good info. If you go to our website, there are links to a lot of information about woods, and wood products, like the National Hardwood Flooring Association, etc, and there is probably something in there about engineered woods.
www.kellogghardwoods.com is where I work.
Planet (from CT)