Of course you can't combine two AWDs. But that's not what OP is asking about.

AWDs and coupons are separate fields, though.

This is FlyerTalk, so we assume you Fly if you're talking here. So let me explain that with respsect to airline promos, AWDs get you the discount while coupons get you the bonus miles. There's no problem using an AWD from airline A with a coupon from airline B in most cases.

However, there are a few exceptions. Some airlines, such as BA, may not award miles for corporate AWDs. And there occasional airline bonuses (like one from WN was within the past year) which need AWD only (for both the discount and the bonus miles), so in that case obivoiusly you can't use another AWD for a different discount and still get the bonus miles.

But I've certainly mixed WN discount with AA coupons (earning AA on that rental) and AA discounts with WN coupons (earning WN on that rental). Generally, the coupon has to match what you're earning, but the AWD doesn't. Just takes care that you don't pick some AWD you don't understand at random, in case it's a "corporate" (or whatever) AWD that doesn't work with your airline promo.