oh yeah i read-up on this article a couple days back.
my family and i do a lot of shabad kirtan at home and at gurdwara and all and we try to use traditional instruments and well as singing in the nidharat raag. in terms of gurmat sangeet, the taus, which was invented by guru gobind singh ji, and rabab (used by bhai mardhana) are used, along with the jori style of tabla (normal purha and pakawaj-style dhama)
i know that the harmonium was used by qawali singers a lot back in the day because their voices were not liked by some audiences and the vaaja it kinda covered up their voices. that's what i researched and discovered, however legends like nusrat fateh ali khan were amazinggg singers and i love their voice, so i don't know how accurate that is.
That being said, the vaaja isn't a great voice-accompanying instrument, compared to string instruments such as dilruba, sarangi, taus, violin, etc. Because, in terms of singing, the voice is able to sing at many different notes and we have the ability to 'slide' between notes and create certain tones that cannot be accomplished by the vaaja and other reed instruments. hence, with string instruments, you're able to achieve multiple tones, similar to the human voice.
here's a video of my sister and i playing the dilruba and tabla, respectively. i didn't really practice for the tabla solo so it's kinda ehh but lemme know
UMBC Tabla Solo