G/S armed is as safe as ALT armed.
But It is possible to fly V/S without ALT armed and forgetting to arm approach. also, it may happen that G/S signal is down.
In the 744 there is not an "ALT armed" selection, but I will assume the concept is the same as setting a target altitude in the MCP.
You contradict yourself in the second sentence. Assuming the autopilot engaged (as in the OP's query), V/S WILL capture the target altitude when that altitude is approached. An insufficient rate of descent may preclude G/S capture, in which case the airplane will impact the runway at the selected RoD. A G/S failure or outage or other anomaly may allow an impact short of the runway.
[quote]One day I remember that we were capturing from above and then something smelled rotten, we realised G/S signal wasn't there! It was a VMC day and we noticed the problem, but in a busier IMC situation, who knows, only EGPWS could warn you of an inminent crash into terrain.
My conclusion is: use the recommended method, but d not capture glideslopes from above in high workload or low situation awarenwss situations due to whatever circumstances. If in IMC, extra monitoring is required./quote]
The problem with that analysis is that it is EXACTLY the "high workload or low situation awarenwss situations" where a pilot might [blindly] choose to roll the V/S wheel down and the altitude wheel up, removing the protections when they are most needed.
If you are worried about a premature capture of the target altitude interrupting a reasonable intercept, then use the ILS minimums as the target, rather than the otherwise suggested 1000 or 500'. At least then you will be within go-around parameters when the altitude is captured.