The Mets have signed the following pitchers and invited them to Spring Training:
It's not likely that any of these fellas will crack the big league roster, but it never hurts to extend an invite, as the Mets have done well in each of the past two seasons with NRI (non-roster invitees).
Ricky Botallico made the team in 2004 and posted a 3.38 ERA in 69.1 innings with 61 walks, 34 strikeouts and just three homeruns.
Last year the Mets struck gold with Roberto Hernandez, who was arguably the Mets' best reliever in 2005.
As for the new guys...
All you need to know about Darren Oliver is that the two pitchers most similar to him according to baseballreference.com are James Baldwin and Eric Milton. I suppose Oliver is still knocking around the league because he's left-handed, since there's really no rational explanation for his continued employment in Major League Baseball. He has had exactly one good year (1994), and his career ERA+ (93) and WHIP (1.54) are, well, James Baldwin-esque (91 and 1.46, respectively).
Pedro Feliciano is a lefty like Oliver and, also like Oliver, he isn't really any good. He is only 29 to Oliver's 35, but there's nothing special about his stuff or his numbers. He appeared in 51 games for the Mets from 2002-2004 before slinging over to Japan to play for the Fukuoka Softbank Hawks last season.
Jose Parra also pitched for the Mets in 2004 before apparently dropping off the face of the planet in 2005. He actually pitched reasonably well in his brief stint in New York, ringing up a 3.21 ERA and a 14:6:2 K:BB:HR ratio in 14.0 innings. His career ERA is 6.09 so I wouldn't exactly expect much out of him.
Octavio Dotel is still out there, though he's not expected to pitch until midseason. Four teams are reportedly looking at him including the Mets and the Yankees, though the word is that he only wants to sign a one-year deal and then hit free agency again in 2006. There isn't much incentive to sign the guy for one year considering he'll only be healthy for half of it, but chances are that he'll sign a one- or two-year incentive-laden deal.