You're absolutely correct. Lots of speaker manufacturers use ferrofluid to provide superior heat dissipation in their tweeters. That way, the tweeter is capable of greater power handling and higher playback levels.
I may have mentioned this elsewhere, but in the old days before ferrofluid ('70s, '80s) in one speaker we reviewed, the tweeter dome (a popular British tweeter) actually began to melt at high playback levels from the voice-coil's heat. The dome's shape distorted and the tweeter's frequency response and dispersion went totally haywire. If you lowered the playback level, the dome assumed its original shape and the speaker's response returned to normal!
File "ferrofluid cooling" under advances in speaker design.
Axiom Resident Expert