There is the statue of Luigi and Daisy dancing together in Daisy Circuit for Mario Kart Wii, which would suggest more than a close friendship. Luigi and Daisy's tag team name in Mario Party 5 is "steady sweeties" which also implies that they are in a relationship, but I'm not sure if the localization matches the original Japanese. Overall Nintendo seems to be purposefully noncommittal when it comes to confirming any Mario Characters being in explicit romantic relationships, especially nowadays.
I'm not invested in shipping personally, but that's the evidence I can recall of Daisy and Luigi dating in the games. There's definitely evidence that supports it, but I could see it interpreted as a close friendship too.