What is the german equivalent of "Dear Hiring Team"? Is it "Liebes Einstellungsteam" ? I was wondering if we could use "Liebes" in a formal letter.
In German formal writing, you either address someone by name, if you know it (e.g. "Sehr geehrte Frau Müller" or "Lieber Herr Maier"), or use "Sehr geehrte Damen und Herren", if you don't.
In informal writing, everything is possible, and there really aren't any rules for it. You can write "Liebes Einstellungsteam", but I wouldn't, as it might carry an ironic or deprecting undertone.
If you are unsure, always use "Sehr geehrte(r) ...". No-one will be offended by it, though some might think it overly formal. But it is better to err on the side of caution. You can always adapt to how you are addressed when you receive a reply, in your next letter. For example, if you write "Sehr geehrter Herr Professor ...", and the professor replies with "Hallo Herr ...", you can write "Hallo Herr ..." in your next letter or email.
When you apply for a job, the recommendation is to find out the name of the person you are writing to, for example by carefully reading the job ad (as it usually contains the name of the person you should write to) or by calling the company and asking who you should send your appliction to, if you are sending an unsolicited application.
We usually don't write "Liebe(r)" when addressing an unknown or not well known person formally, especially not when asking or applying for something. There normally has to be some kind of personal bond before we write "Liebe(r) ...".
"Liebe(r) ..." is sometimes used to pretend or to establish that there's a bond though. For example, businesses might use "Liebe Kunden" or "Liebe Frau Müller" to address their customers, political parties or clubs (Vereine) might use it to address their members ("Liebe Genossen", "Liebe Parteifreunde").
The formal way is usually "Sehr geehrte Damen und Herren" or "Sehr geehrte Frau Müller". As @lube already wrote, as an applicant, I would either try to find a person that I can address with "Sehr geehrte(r) Herr/Frau ..." or write "Sehr geehrte Damen und Herren".
Additionally: "Einstellungsteam" is not a word that I have heard before. The classic word would be "Personalabteilung", and I have sometimes heard "Recruiting-Team", too. However, this is not something that I would use in an address in an application.
In industries where formalities are frowned upon, a "Guten Tag" may also work if you don't have a single person to address, or maybe even "Lieber Herr ... / Liebe Frau ..." if you know a person and have already spoken to that person before. Still, don't address a whole team that way.