My question is in regards to a Hadith from Imam Ali(as) in which he says: It is incumbent upon God to cure one who conceals his ailment and complains only to Him.

my question is: can we act on this hadith, seeing that doctors today often emphasize the immediate treatment of some ailments.

I would understand this Hadith to be regarding spiritual ailments and not physical.

As we have narrations saying that for every ailment Allah has created a cure. And we have to take care of our health.