If it's purely wet grass than yes, chains will help. I know how slippery dew covered grass is and 2wd can be almost useless on it. However, if the ground is soft, which it sounds like it is in your situation they aren't going to help. If the truck or especially the trailer starts to sink in even an inch or less you will be doomed and a 4x4 probably would be too.
A truck with 4wd can usually go through the mud pretty well if you keep moving, attach a trailer to it and not so much. As soon as the trailer starts to sink you are attached to an anchor.