No Inde does not have a ballroom, Small dancefloor with a live band in the Viking Crown Lounge, or a Salsa type band in Bolero.
I too love ballroom dancing and without any doubt you need to sail with Cunard. QM2 has biggest ballroom afloat and a dedicated dance band (that does'nt double anywhere else). There you go, Richard.
I agree that QM2 is probably your best bet as the Queens Room has a huge dance floor and live band and on the whole doesn't appear to be used for anything else.