Yes, Pikachu is able to learn Dig. It can learn Dig through the use of the Dig TM, which you can buy at the Cerulean City Poke Mart.
I know that Pikachu can learn dig. I also think it's true that Aron can learn dig. I hope I helped you!
caves
Yes, Linoone is able to learn Dig by TM.
Some Pokemon that know, or can learn Dig: Sandshrew, Sandslash, and the Mightyena that I have knows Dig also.
Sandslash learns Dig at level 30 in Pokemon X and Y. In Pokemon Omega Ruby and Alpha Sapphire, it can learn Dig at level 33.