There's a run line on bases, which is simply betting a team will win by -1.5 or vice versa (so you're saying they will win by two runs or more). But there's not a spread like in football or basketball, because the scores just aren't as high.
Betting a +1.5 is not recommended, as you're basically saying a team will lose by exactly one run, and paying extra for it in the process. If you think a team will win, bet the ML. If you think they might lose by a run, don't waste your money.
Dsethi (I believe) had an interesting formula for betting -1 lines by betting some on the ML and some on the run line, though I am far from qualified to try to explain it at this time.