Can I still be attacked while Hiding?

The Hide card prevents you from being targeted by an opponent. Cards that don't use the target keyword, or cards like Axe-ident which cause you to target yourself (you are not an opponent of yourself) can still effect you while hiding.

Can I play a Blocks-A-Lot-L against a Blocks-A-Lot-L?

If you use a Blocks-A-Lot-L to deflect an Axe-A-Little to another player, the Axe-A-Little is still in play, and just being directed to a new target. So if you have an Axe-A-Little deflected towards you with a Blocks-A-Lot-L, you can play your own Blocks-A-Lot-L to deflect it back (or to a different player). The only limit to the number of times an Axe-A-Little can be volleyed around the table is the number of Blocks-A-Lot-L cards players are holding.

If I use an Om Nom and draw another Om Nom, can I play it?

It is possible to draw an Om Nom as a result of an Om Nom, and yes, you can then play the second (or third) Om Nom for even more cards. You can hold as many cards as you want during your turn, but at the very end of your turn, you must discard down to four.