My experience is that it’s not really specific to the equipment. Anything that you put in the room (particularly near the speakers) can have a positive or negative effect on the room’s acoustics.
I can imagine a scenario in which an equipment rack could be open and highly diffusive, and might have a positive effect.
I can also imagine a scenario in which an equipment rack could cause awful first reflections and have a negative effect.
There is also the issue of having equipment so near speakers, that more than usual levels of vibration are introduced. This would be particularly bad for tube equipment microphonics, or turntables. As for solid state electronics, that gets us into the realm of religious debates, and is probably best avoided.