A few days ago I noticed a couple of bees frantically going from each bee coming home (so I assume they are guards) but every 3rd or 4th bee they greet they kind of climb on or get very close to and they (the assumed guard) shakes/vibrates for about 1 second.
Also the assumed guard quite often bounces back end and is grooming hind legs.
I saw a video on Youtube of bees doing a grooming "dance" and my bees are doing the same moves but they are also doing the shaking/vibrating thing.
I have been feeding via entrance feeder so maybe they are just asking to be groomed???

After 3 days I am noticing more and more doing it

This is a swarm that moved into this hive on July 4th

Hive was FILTHY before they moved in. Got into it last week and changed bottom board and checked a couple of frames and they did a great job cleaning.

I've been feeding syrup (1 to 1) for a week. They have now stopped taking it.

Other then the shaking/vibrating thing they appear to be doing great. VERY mellow girls. Today I added some Popsicle sticks to inner cover for ventilation and pulled two frames just to check em out(tons of brood) and never once used any smoke.

So my stupid question for the week is:
Could this be a harmless dance?
Could this indicate a disease?