Alejandro didn't dance with Elena merely to flirt with her - he did it to attract Don Rafael's attention towards them and get back into the circle of Dons. There's very clearly a glance exchanged between Diego and Alejandro, right before he asks Elena for the dance. He then chose the most risque dance he could to make sure Elena's father would come down.
There is some hilarious Fridge Logic resulting from this — Both of the above characters are quite certainly of pure Spanish ancestry and played by actors from the UK, while the mestizo Alejandro is played by authentic Spaniard Antonio Banderas.
A bit of Fridge Brilliance: at one point in the film, Elena's old nanny (though she doesn't know it yet) speaks Spanish to her — which a young girl nearby has to translate, because they've been speaking English the whole time. If Translation Convention is in effect, they're already speaking Spanish, so what is the nanny speaking? An indigenous language, since as the nanny she'd be from the poor, indigenous class.
The nanny is actually speaking Nahuatl, an indigenous language from Mexico, still spoken by millions today.
Which doesn't make much sense, since Nahuatl is spoken mostly on the center states of Mexico (Estado de Mexico, Guerrero, Puebla...), really FAR away from California, where Esperanza, Diego and Helena lived. So it's more probable that it was Yaqui, Seri or even Raramuri (Tarahumara) languages, which are northern Mexican indigenous groups. Although all of these groups are Proud Warrior Races, more than the center and south Mexico groups.
In certain fight scenes, there are people in the background going on with their work while the fight is happening. When Diego approaches Alejandro in the bar, the bartender shuffles away quickly when Diego gives him a glare. The Fridge Brilliance is the subtle way the film establishes why Zorro is so beloved by the people: he's the only one who doesn't ignore all the violence going on in the world.