Ammonium sulfate might not substitute amonium per sulfate (APS) as APS is source of radicals however ammonium sulfate do not.

No,

Ammonium sulfate can not be used in place of APS

No, you cannot use Ammonium sulfate in place of APS.

Ammonium Sulfate cannot serve the job of APS

No, many students tried this in my lab not beeing able to read the names on the tubes correctly. It never worked for the given reasons.

Surely, Ammonium sulfate can't be substitute of APS

Agree, ammonium sulfate can't b used.

Thanks to all for your kind answers and yes, I got the point.

No, not at all.