One point worth noticing : since some time now (don't remember version), electrum client doesn't connect to a single server, but to more. That's for getting block headers and notify the user if a certain server lags some blocks. In that context I don't know if it worths connecting to a hidden service, since your client will further connect to different "normal" nodes.
Observe :
electrum directory /home/stepkrav/.electrum
blocks: 290884
wallet path /home/stepkrav/.electrum/wallets/default_wallet
connected to electrum.hachre.de 50001
connected to electrum.cryptopush.com 50001
connected to 56ckl5obj37gypcu.onion 50001
connected to electrum.no-ip.org 50001
sending subscriptions to 56ckl5obj37gypcu.onion:50001:t
connected to ecdsa.org 50001
connected to h.1209k.com 50001
failed to connect electrum.stupidfoot.com 50001
connected to electrum.novit.ro 50001
synchronizer: connected to 56ckl5obj37gypcu.onion:50001:t
Notifying GUI
Of course your subscriptions will be sent to the hidden service you selected. Don't know. I guess it depends on your threat model.