Would A 301 Redirect At Domain Level On Old Sites Be Enough To Keep The Organic Search Traffic Flowing And Protect Current Google SERPs Rankings?

In episode 171 of the weekly Hump Day Hangouts by Semantic Mastery, one viewer asked if a 301 redirect at domain level on multiple old sites be enough to keep the organic search traffic flowing and protect the current Google SERPs rankings.

The exact question was:

Hey guys. Have a client with 10 brands in one niche, each with its own site.
Client wants to re-organize so we need to move all the old brand sites to a sub folder on a new domain. newdomain.com/oldsite1, newdomain.com/oldsite2, etc..
Would a 301 at the domain level on each of the old sites be enough to keep the organic search traffic flowing and protect the current Google SERPS rankings?
Anything else you can recommend or advise me to look out for?
Thanks in advance for any help or advice!