Is SHA-1 safe for signing ECDHE parameters?
SHA-1 is still thought to be secure whenever collision resistance isn't required.

The hash is both used for signing certificates and ECDHE public keys. There's however a difference with regard to collision attacks. It is possible for an attacker to attack the collision resistance with certificates by getting their own certificate signed by a CA. In ECDHE however the attacker shouldn't be able to control the ECDHE public key parameters that are signed.

So, while I wouldn't recommend using SHA-1 in new applications if you can just as well use another hash, TLS is what it is and this kind of a cipher suite is still thought to be secure.