Yes he did in the vernacular, but it's more important to call it for what it is in legally indefensible terms. "Smear" is not a legal term.
At first, I thought Limbaugh was "slandering" her, but then saw this legal definition:
slander
n. oral defamation, in which someone tells one or more persons an untruth about another, which untruth will harm the reputation of the person defamed. Slander is a civil wrong (tort) and can be the basis for a lawsuit. Damages (payoff for worth) for slander may be limited to actual (special) damages unless there is malicious intent, since such damages are usually difficult to specify and harder to prove. Some statements, such as an untrue accusation of having committed a crime, having a loathsome disease or being unable to perform one's occupation, are treated as slander per se since the harm and malice are obvious and therefore usually result in general and even punitive damage recovery by the person harmed. Words spoken over the air on television or radio are treated as libel (written defamation) and not slander on the theory that broadcasting reaches a large audience as much as if not more than printed publications.
bold in text mine
Apparently - and any lawyers out there will please correct me - the definition of "libel" pertains to written statements. The term that best applies seems to be:
libel per se
n. broadcast or written publication of a false statement about another which accuses him/her of a crime, immoral acts, inability to perform his/her profession, having a loathsome disease (like syphilis) or dishonesty in business. Such claims are considered so obviously harmful that malice need not be proved to obtain a judgment for "general damages," and not just specific losses.
I think it's important to use the word "libel" (or "slander") because that is the legal definition of what Limbaugh did to Sandra Fluke. Undoubtedly, Limbaugh's non-apology was intended to avoid a lawsuit as well as the loss of sponsors. Words matter. Do you think Frank Luntz would use "smear" instead of "libel" or "slander"? I don't. He'd go for the harshest words.