Pretty much zero ppm ph7.
Yes I've tested my dehumidifier water. Lol.
The only issue could be if you don't keep the tank etc clean.
I mean come on, who strips their dehumidifier down to clean it properly? I know I don't. This could possibly harbour bacterial growth of a bad kind.
But if everything is cleaned and disinfected regularly then it can work.
Extra Ca and Mg would be needed just as if you were using RO.