If so, is it safe to use the Electrum 2.6.4 version now ?
Yes, but I won't advise to use it to hold large amounts of funds.
If you have substantial amount of coins I would really advise to use HW wallet (apps) or use "Electrum Dash + HW wallet" combination, so that your private keys would never touch any online machine or stored in any kind of internal software db. Electrum Dash works with Ledger and Trezor.
I second this.
https://electrum.dash.org/ BUT they are NOT signed (afaik), a proper release process is yet to be established, so use with caution if you plan to store coins without HW wallet there.
Finally, I've got it working on MacOSX too, so soon the final build scripts would be released.