1. Actually, when Celtic cuts Grid's tail, its wristblades melted almost instantly after the cut. This was then contradicted in the same movie by Scar cutting half of an Alien's head off and suffer no damage to its wristblades. The movie actually contradicted itself here.
2. Again, the same as above. Though it could be argued that some of their equipments are made to be acid-proof, the question is why don't they make other weapons which are just as important (such as the nets) acid-proof.
And also, the shuriken that was thrown by Scar to the Queen didn't take any damage from the acid either.
"There are five possible operations for any army. If you can fight, fight; if you cannot fight, defend; if you cannot defend, flee; if you cannot flee, surrender; if you cannot surrender, die."