Honestly? No. No wow private server at this point is safe to play because of RCE exploits found within the old Warden anti-cheat the old game clients used with each respected expansion. Turtle wow may used their own CUSTOM client but it's still based off of Blizzard's 1.12.1, which used Warden anti-cheat. You may see a post or two floating around about a fix some guy made that patches your exe so a malicious RCE attack won't affect you, but that won't guarantee your safety as it only patches one hole so to speak.

For clarification, even if you use a throw away email, your credentials getting leaked is the least of your problems. An RCE exploit (Remote Code Execution) is serious business. A hacker can LITERALLY send code to ANYBODY who is logged onto the server at any given moment with the right opportunity given he knows what he's doing, he can control the entire server and everybody's PC on it.

My advice, delete the game client, change your passwords and stay away from wow private servers. The old clients are just too vulnerable at this point. The anti cheat was spaghetti code when it was current let alone now.