Up to the DM
There is no explicit defintion in the rules what counts as "wiedling" a weapon. I can see two different lines or reasoning, one for, and one against unarmed strikes counting as wielded (the one for it somewhat indirect). Since the rules do not resolve this -- at least to my knowledge -- the DM must resolve it.
Definition of wield
The English language defintion of "wield" is
hold and use (a weapon or tool). (Oxford dictionary)
to hold a weapon or tool and look as if you are going to use it (Cambridge Dictionary)
so the defintion means you need to be able to hold the weapon. By this logic, as you cannot "hold" an unarmed strike, it cannot be a weapon you wield.
Usage of wield in the rules
The vast majority of cases the term wield is used in the rules, it clearly refers to a weapon that is an actual object.
However, the Weapons section of the SRD contains a table of weapons that lists unarmed strike as its second entry and that is prefaced with the following introduction (emphasis mine):
Weapons found on Table: Weapons that have special options for the wielder ("you") are described below.
If unarmed strike is a weapon and has a wielder, than it is a weapon that is wielded. Now, it may be that they used this language because it applies to the majority of weapons in that table, and not to define that an unarmed strike counts as a wielded weapon, but they could just as easily have said "the user" to avoid this issue.
A manufactured weapon is defined as
in essence, any weapon that is not intrinsic to the creature.
The monks attacks count as a manufactured weapon for spells and effects that enhance or improve either manufactured weapons or natural weapons. However Holy Strike does not improve manufactured weapons, it improves weapons that are wielded. So I think wether the the Unarmed Strike counts as manufactured or not is a bit of a red herring in this context: a manufactured weapon is not affected by Holy Stike, unless it is also wielded.
In any case, while I think the intent is probably that a wielded weapon is an actual physical object that you hold in your hand(s), there is enough room for doubt to defer the decision to the DM.