The issue isn't the amount of memory, it's addressable space. LMDB maps all on disk data into memory. If that value exceeds the process addressable memory, you will get a critical failure. On 32 bit systems, process addressable memory maxes out around 2~3GB. Therefor, any file LMDB uses that exceeds 2GB in size cannot be created nor used on a 32bit system. This is a long winded way to saying please don't try this.

If you insist on attempting this setup, you should do it the smart way: create a 32bit VM of some Debian flavored distro, the closest you can to the target Raspbian version. Give this VM a copy of the blockchain, then build the smallest existing Armory DB on that VM (db-type=DB_BARE). This will give you a ~200MB database. Then take this DB with the relevant copy of the chain your Pi and cross your fingers.