Is placement of vinyl over concrete then using bostics best enough to retard moisure when using a 5 inch hickory engineered plank.

Yes, it is! It is one of the tried and true moisture barriers. However, it must be done properly. Use a low end sheet vinyl and a quality multipurpose flooring adhesive compatable with vinyl flooring. Level and flaten the concrete slab first. Bostick's also recommends roughing up the vinyl surface a bit after it's installed to aid in adhesion. I use my floor buffer and a used 100 grit screen but you could use a small vibrating sander and some fine sandpaper. Or even a sanding pole like the sheetrockers and painters use. You just want to knock some of the gloss off.

Kimberly,
You could go a step further and require that the sheet-vinyl be adhered with an acrylic adhesive instead of the basic, multi-purpose. This will insure you somewhat in terms of pH levels that attack regular multi-purpose adhesives.

It will cost you an addititional 1-3 cents a foot. Pretty cheap insurance in my book.