Tomahawks WERE actually used in Vietnam as weapons by some Special Ops people, including Special Forces, Rangers, and especially Marine Recon.
It's particularly within Marine Recon were the tomahawk seems to have been a favored weapon, and apparently, still is.
They were indeed used as anti-personnel weapons, and they were indeed VERY effective.
During the war an Army Captain recommended replacing the bayonet with a tomahawk and gave a demonstration of the capabilities of it to a group of senior officers.
This Captain was absolutely deadly with the weapon, and showed just how effective it could be as a sentry-removal tool, hand-to-hand combat weapon, AND as an effective counter to a bayonet.
He recommended replacing the bayonet with the tomahawk because it was clearly more effective and flexible than a bayonet, and could be used both as a tool and weapon.
The officers were particularly astounded by the Captain's demonstration of the various ways the tomahawk could be used as silent-killing weapon.
They noted that in demonstrations of the tomahawk versus bayonets, knives, clubs, and unarmed hand-to-hand combat, the users of the other weapons stood no chance against the Captain and his tomahawk.
The general officers all agreed that the tomahawk was clearly superior, but discounted it because of the additional training needed to become proficient, and what they called the "Non-military" image of the weapon.
This Captain also gave demonstrations to Special Ops units, and they were taken both by the effectiveness and by the elite image.
From all accounts, the Special Ops people made excellent use of the tomahawk, but like the use of silencers and other "Special Equipment" most accounts only allude to the use of such non-standard weaponry.
Reading books by Vietnam vets of Special Ops units like SEALs and Special Forces, you'll note quickly passing references to "Special Equipment".
Most of this is still-classified equipment, but some of it is non-standard weaponry like cross-bows, garrotes, and tomahawks.
Apparently, the tomahawk is still being used by some Ranger and Marine Force Recon personnel, but again, due to Political Correctness, the use is being downplayed along with all the other "Special Equipment".
True, MOST of the tomahawks used in Vietnam were tools or used to hype the image of troops, but a number WERE highly effective weapons, and if you read and listen closely enough you'll note the references.
Like most elite forces, the REAL people don't talk about their activities and you won't be reading any first-hand accounts about slaughtering VC and NVA troops with tomahawks, OR garrotes and other non-PC weaponry.