Both Esther Williams and Ricardo Montalban are on record that the song was indeed suggestive:
The actor assigned the part of the wolf in the film duet was Ricardo Montalban. His first language was Spanish, and he later explained that he did not realize during filming just how suggestive the lyrics were. Esther Williams was amazed that film censors allowed the song in the film, saying: "Baby, It's Cold Outside!...really was suggestive."
Google Books: You Ain't Heard Nothin' Yet Interviews with Stars from Hollywood's Golden Era
And contrary to representations now being made by its benighted apologists, some were troubled by the song when it was unleashed in 1949:
Google Books: You Must Remember This 1949
Yeah, yeah, it's suggestive. It's suggestive that the guy wants to have the woman stay a bit longer and maybe get into a makeout session with her. It's not suggesting that he's put date rape drug in her drink, it's not suggesting that he's going to rape her. It's light banter and flirtatious repartee.