Isn't it není "It isn't"? Wouldn't it be It isn't (ever) never good to hate
In english you can have only one negation in a sentence.
To add on to what ValaCZE was saying, in Czech, double negatives enforce rather than counteract.
Can I use dobře instead of dobré?
No. You want the adjective "good" here, not the adverb "well".
"To" is not necessary in this sentence? Is it a mistake to say "Nikdy to není dodré nenávidět."?
The "it" in the English sentence is a dummy place holder. Compare the following two English sentences:
1. It is never good to hate.
2. To hate is never good.
So even in English you don't need the "it"!