Yeah, I don't think he's a bad guy to take a flyer on but I'm not so sure he's out of the woods with his injury problems yet and would be a little concerned about that even though he is only a DH.
(Note: He played 3B today in Spring Training and, just to prove he can't catch a break with injuries, he got a minor one today when he got a gash in his forehead diving for a ball!) http://texas.rangers.mlb.com/news/artic ... p&c_id=tex
Anyways the thing to remember is that he went on an absolute tear to end his '08 season, and homered in 5 of his last 7 games. This was after several injuries as I just saw on his Sportlsine update, which states: "He originally strained his left hamstring in April, then developed carpal tunnel syndrome on a minor-league rehab assignment and needed surgery on his right wrist. Then, back on his rehab assignment, he hurt his right hand diving for a ball, and when he finally returned to the majors, he had to go back on the DL with right shoulder inflammation."
One crucial thing to note though is that he went on this hitting tear in Sept. after all of these injuries, so it seems he was right back to being healthy... and this spring, he's 10-for-35 with 2 homers, 2 doubles, and a triple so even if it's against ST-styled pitching it appears he's driving the ball with authority.
Again, I'm not sure if I trust the dude to stay healthy, but I like the odds better with him being DH only (and judging from the news above, he should probably think twice before running out to play third base
I would still much rather have a sure thing like Aramis at the hot corner, but if you take both of them and wait to see if Blalock ends up panning out then you can do as you suggested using Aramis as trade bait. Unfortunately the day after you make that trade, Blalock will probably get injured again. I also know that this isn't the right forum for the trade question but since you mentioned it, I do think you're not getting quite enough for Aramis because as good as Bruce/Johnson are, because even though they're quality players, they haven't proven themselves over the long haul like Aramis has.
Good luck to you. I'm glad you posted this 'cause it got me interested in researching Blalock a little bit and has almost convinced me to go the extra buck on him at the end of my auction tomorrow!