"...the ants walked over the line and fell immediately into convulsions and died" - that would likely mean that, after a few had done that, the other ants would see what had happened and avoid it, and keep out of the monk's space. So most of them would survive, and he'd have an ant-free corner.

I'd call that a reasonable compromise rather than "meretricious hypocrisy". ("Meretricious" - meaning, I take it, that it looks good, but doesn't stand up.)

If it was a slow acting poison so they all marched through and died later, it'd be a different matter.

My impression is that Buddhists tend to be fairly flexible on these kinds of thing - being totally rigid is rather un-Buddhist.