Taxi drivers are mainly worried about People being sick in their cab , people who don't pay or people who assault them.

All taxi drivers I have known have met all kinds of somewhat crazy/scary people I would really have a hard time believing that a gay person would be the slightest bit controversial.

Of course there is always some risk but if it is large enough that you are seriously concerned about being randomly assaulted just for being gay you have probably chosen a bad place to live.