Not necessarily, but it sure will make your life immensely easier. If you’re only building 1-2 months per month, you can probably do it yourself or someone in your team with some free Youtube education. It’s not rocket science. Getting the details right has its own learning curve of course, and it’s a little steep. You can always hire someone to do outreach (if they are good at it, which isn’t easy, or if you can train them), someone to write your guest content, someone to track the whole thing (links, payments, rankings, etc) and pay the link invoices etc (expect to be always asked for money by the publishers, even if sometimes they don’t, because it’s so common… so its’ not like it’ll be free)
If all of the above sound great then you can probably do it in-house. If it sounds like the potential for you to get it wrong and waste a ton of money is high, its because it is. If it sounds horrible and you don’t want to deal with ANY of that, get in touch!