What I'm hearing here are, I think, two different scenes: the first where you are hiring another company to assist you with your drafting, and as such, it has to meet your drafting standards. The second is where you are hiring a sub to furnish something that is there specialty, such as furnishing you with, say HVAC drawings for your buildings. In this second case, you may have difficulty in getting the sub to deviate from their own in-house standards. Just as you don't want to deviate for what works for you, the sub may feel likewise.
But......All it takes for an enforceable contract is for the two parties to agree to something, put it in writing, etc. And if you can get the subs to agree, then done deal.
I would suggest writing up your drafting standards as an exhibit that can be referenced in the contract and attached to the contract, just like you do with, say, your standard hourly rates sheet. Then the standards can be varied from contract to contract to keep up with changes or job types.
It's Friday afternoon and I'm writing about contracts? Jeeze, Bob, get a life or go home. Seriously, though, contracts is important stuff and worth all the time you spend on them. G'luck.
Bob