Dan's in a deep N.L.-only league and wants to know whether or not a few middle relievers are worth adding. OK...
If you're a run-of-the-mill minor leaguer, picking up a save in an unsettled bullpen is a great way to garner attention. Guerra's minor league profile doesn't indicate anything special. He's got a decent fastball/slider combination, but has a history of command issues and shoulder inflammation. He seems to have ratcheted down the walks this year but at the expense of his batter per inning whiff numbers in the minors. Guerra's OK at the back of your bullpen I suppose, but even in a deep league, I suspect you can do better.
Dan most likely asked about Lindstrom because Huston Street is sucking wind this month. The 6.52 ERA bothers me far less than the 5 HR allowed in May. Lindstrom has been great for the Rockies and if they do decide that Street needs a breather he should step in and gobble up the save chances. The BABIP screams regression and the K/IP do not speak to dominance, but opportunity is more important here than ability. Definitely grab Lindstrom if he's available.
Elbert's days as a high flying prospect are long gone, but his strikeout ability and left-handedness should keep him in Major League bullpens for years to come. The problem with Elbert as a Roto proposition is that the Dodgers are using him as a LOOGY. It's hard to generate value from relievers who average well under an inning an appearance no matter how good they actually are. Leave Elbert on the wire.
I have Bastardo in Tout Wars so I obviously like him and think he's roster-worthy in deep leagues. He has the same caveats that Lindstrom does about the BABIP, but Bastardo's K/IP is ridiculous and makes his shortcomings in real life forgivable. He's not going to close, but Bastardo's high whiff totals mean you should add him in 5x5 if he's still out there in your N.L.-only.