i'm not sure about the pods. but all three of my mercs loved snails and hermit crabs. I also feed them frozen shrimp when i could but they can be quite reculive and sometimes i just couldn't find them to feed them. i think my problem was i had them in a tank that was too big.
After keeping many mercatoris, I swore they would not eat table shrimp but my last little female (Sleazy) proved me wrong so it is worth a try (in small pieces) when the octopus if fully grown. I think table shrimp is too tough for young ones (of any species) but at some point it appears even the mercs will eat it. Be aware that often any species will stop eating table shrimp near the end of their lives and again, I think it has to do with it being too tough.
I have never had any success offering the krill that is frozen as fish food. However, we recently found frozen "baby shrimp" at an international market that I belive are krill and these are well received by all the octopuses we keep. The "baby shrimp" we found are about the size of shore shrimp and mostly whole (shore shrimp being another good choice, but expensive and often to be freshly killed or frozen for a regular meal but providing a few live in the tank offers a little hunting, an occassional catch and a bit of clean-up crew).
Fiddler crabs, alive or frozen are almost always accepted by any species, including O. mercatoris.
Shelled hermit crabs have been very successful (some have reported that their mercs will raid and eat live ones in their shells but I have not seen this). They are hard to remove (even when dead) from the shells and we resorted to freezing them to euthanize and then cracking open the shell to feed (still requiring a knack, especially if they are not large).
I feed all my tanks frozen (not dried) Cyclop-eeze and the color of the poop shows that all my octopuses either eat it or eat something that does (pods). I have a video of Trapper, post egg hatch, sucking it in from a pipette.