Yes, in some companies subcontracting is very common. Particularly in Japan. Tose does contract work for an unbelievable number of companies - some Japanese studios consist only of concept artists and designers. Mistwalker outsources almost their entire engineering process.
From Gamasutra's Interview: Tose: Game Development Ninjas:
GS: How many people do you employ?
MA: 800 in Japan, 200 in china.
GS: How come we've never heard of you until right now?
Koichi Sawada: Well we're based in Kyoto, right? So we're ninja. You can't find us! But in the past 26 years we've worked on 1,100 games. Including partial games.
GS: Do you have a breakdown of what percentage of your staff does what?
SC: Our Chinese operation has a higher percentage of partial work, whereas the Japanese studios do more full development. Companies come to us if they need models, or maybe some animation. Right now, we're also making all of our artists in China hybrid artists. Which means they can do both 2D and 3D, so that at the end of the year, every artist should be able to do 3D art.
GS: How many dedicated 2D artists do you still have in China at this point?
SC: Maybe about 40.
GS: In Japan what are the majority? Programmers?
MA: Programmers and artists.
From Return Of The Ninja: Tose's Stealthy Outsourcing Progress:
How many developers are working at Tose, now that you've opened more studios?
It's 1,000 in Japan, 200 in China, and two in the U.S.
Are there any plans to do any more original IP out of Tose in the near future?
We already make original games for publishers, but we will not own the IP of that project.
Will it be based on ideas generated from Tose, or from the publisher?
From both. It depends on the project.
Note that Tose isn't doing mobile and web games, for which outsourcing is well-known - they're doing A to AAA games, sometimes the entire game, and having the publisher take credit for it.