Marco,
I think that the only advantage to putting tea in the mix would be that it would raise the acidity, and I think that fertilizer already does that pretty well. And, I suppose that if it were decomposed a bit, it could add some nutrients, but if you're already fertilizing, seems unnecessary. The caffeine will will some pests, too... don't know what it will do to the orchids.
BTW, Earl Grey has bergamot oil in it (though in small amounts) which is a citrus oil... might work like Neem. Or it might kill your plants
- Matt