No, it's not okay if Trump did it.
That type of reply, which is clearly intended to do nothing but deflect away from the original point that was made, does nothing to persuade anyone that HRC didn't ignore the desperate cries for hours, for help from a US embassy that was under attack.
If you want to talk about the situation in Niger, then talk about it. Questions that could legitimately be asked include, but are not limited to: Why were the soldiers there? Does the policy that put them there need to be revised or abandoned? Was Trump disrespectful to the families of the soldiers lost when he spoke to them? Those are the types of intelligent questions that lead to an intelligent conversation
Just using the 4th grade tactic of saying something like "oh yeah, well you're one too" doesn't accomplish a damn thing.
And that doesn't even get into discussing whether or not using the situation in Niger for a 'compare and contrast' with what happened in Benghazi is even an apples to apples comparison. The closest thing, imo, to that would be comparing Trump saying the soldiers knew what they were getting into, and HRC saying what difference could it possibly make now. Neither is a very good optics for people who are supposed to be protecting our embassies and their staff, and caring about what happens to our service personnel.