Vlad: Game models are normally made as quads then converted either manually or automated into tris, or they can be made from scratch straight as tris, but it isn't really good work flow having lots of both. I am stating what I read from books I am currently reading, other than me scan the pages I suggest you get them yourself and have a read through.

Though, like you said using tris to add geometry at times is the most effective way. I suppose it depends what this guys model is for as to whether he could get away with slack edge loops and stable polys.