Is it possible to share blockchain data between multiple nodes? I'm planning to create a Raspberry Pi Cluster in order to run several bitcoin nodes. Can I share parts of the ~/.bitcoin/ folder in order to not have to store the entire hundreds of GB for each of the nodes? My idea would be that one of the nodes has an external hard drive with the bulk data and the others make use of it over nfs or smb. 

Any ideas or even experience on this?
I don't think this is possible; you'd have multiple node instances trying to read/write a single data directory. This is not the intended operation, you'd likely end up with corrupt data. 

If you must run multiple independent nodes and are worried about storage requirements, I'd recommend looking into 'pruning mode', it will limit the storage requirements for each node instance. 

Note that you can copy the data directory folder of a synced node, so that you will not need to run through the initial block download and sync for each individual node (lots of savings in time and computation here). Just be sure to stop bitcoind before copying the data directory, and then start it up again once the copy is complete. This will help avoid potential data corruption/loss.