Oh... Sure, man...
Here's how you want to mark something underwater:
http://www.fifthd.com/divestore/classes/video/shootbag.avi
If you take a dumbell down with you, then:
1. You can only carry one or two before you start to run out of space.
2. Keeping them streamlined is a problem.
3. The buoyant little dumbell changes your buoyancy characteristics, which can be a problem especially if you carry them in the wrong spot.
4. If you accidentally let one go, you can't get it back - well, not easily, anyway, which is especially a problem in deep water.
5. Dumbells have the line on them - that is, they uncoil as they go... You hold one end of the line and then let the whole shebang go. If there's any current, once that dumbell hits the surface it'll splay all the way out, becoming a hazard to yourself and others; it also doesn't do a very good job of marking your point for your GPS.
Lift bags, on the other hand:
1. Are streamlined prior to deployment and don't mess with your buoyancy and trim.
2. Can be carried as multiples.
3. Don't get lost if you drop one - they only "go" after you've inflated them.
4. Rise directly above you, and allow you to measure out exactly how much line you want.
5. Double as a surface marker buoy.
6. Can lift large objects if you need them to.
7. Provide a redundant buoyancy source.
In terms of body searching, though, I wouldn't recommend the use of either.
A diver doing a body search in a diver-sized area should be doing it with a line... Like a spool or reel. Almost always, the body will be in zero vis water unless it's in a cave or wreck - otherwise they'd have found the body already.
Anyway, so a diver does a circular pattern search using a line - once the body's located, the line should be tied off to the body, but left in place. The searching diver then returns back up the line (the other end should be attached to an anchor, the rescue boat, a stationary buoy, etc. - or another diver in a pinch) and then acends to the surface with critical information and to discuss with the authorities the condition of the body, the location of the body, and to obtain permission to remove the body from the water. Depending on the situation, the body should never be "marked" directly - no buoyant devices should be attached to it, for fear that it'll get dragged to the surface by wind and current, destroying a possible crime scene.
For that matter, imagine the horror of family members standing on the shore or on the boat - your buoy takes off, dragging a partial body to the surface. Not good.
Besides, once you've found the body, you'll probably be asked to bag it and then lift it, likely on the leeward side of the rescue boat. This means that you're going to have to go get a body bag anyway, unless you plan to do your entire search with one. Getting the chance to go back, discuss the situation with the Captain, and make a mutual decision on what to do now that you've found the body (which may change with whatever information you bring up with you) are all things that you need to stop and have the chance to do. During this time, if you have a marker buoy in the water, people (family members and onlookers) start freaking out, wondering why you're not immediately recovering the body. Thus, no markers should be used.
Low key is "the" key.
It's a matter of respect for the family and a matter of respect for the powers in charge of the operation.
