You can definitely use it for the real Bitcoin.
Have you installed Bitcoin Core? Do you, perhaps, run a node using pruning?
Finally, for the RPC explorer, I think it works with Fulcrum, but I need to check to be sure. I 'll do in the next hours and let you know.
Yes, I have Bitcoin Core running with txindex=1, so no pruning; however, my connection is so slow so I am still only at blockheight 462,528. Since BTC RPC Explorer allows the use of an Electrum server, I have this in my config file for it (which is the address of Fulcrum):
BTCEXP_ADDRESS_API=electrum
BTCEXP_ELECTRUM_SERVERS=tcp://localhost:50001
But it's refusing connections when BTC RPC Explorer tries to use it; perhaps because my Bitcoin Core is still not fully synced? Please do let me know if BTC RPC Explorer and Fulcrum work together!