I tried to enlarge the photo to see what you are referencing but could not see anything. If the hole you mentioned is between the two teeth, then it could have been a piece of cement that was pushing the gums back in this area. If this is the case, sometimes the gum will fill in...
There are technically no such thing as "no prep" veneer. Veneers are an irreversible procedure, in order to bond the porcelain to the tooth, at the minimum a roughening of the enamel by either a "bur" or chemically by acid etching . Please ask your dentist if either has...