Nimbus people haven't appeared in any other game even as an easter egg to my knowledge. They certainly haven't become as abundant as say Lakitus or other series mainstays.
A single lakitu appears to be in the thrall of King Nimbus, the "Royal Bus Driver" (that's a bus?). However there are Lakitu all over SMRPG and most do not appear to have any affiliation to the Nimbus people so I wouldn't jump to make any association beyond "Square/Nintendo thought it made sense for a Lakitu transport in a cloud land".
Note that, possibly due to Intellectual Property issues with Squaresoft (now Square Enix), almost no characters/species introduced in Super Mario RPG have crossed over into future Mario offerings, despite Paper Mario being a perfect opportunity as a somewhat successor and frequent fan requests for Geno in Smash Bros.