I'm a content agency owner that works almost exclusively with SaaS companies, and yes, it works. There is plenty of demand (we went from $0 to $80k/mo in revenue in the first year).

What worked for us was:

1. Going super-niche - we only serve series A and B startups that want to use content to reach software developers. You'd think that going niche would make it harder to find customers, but the opposite is true.

2. Started with my network and referrals. Do good work and people will refer you to others.

3. Build a process that can scale beyond just you.

Good luck!