No. There are several technical reasons for why. I won't go into all of them, but among which; it's impossible to use the stock engine for some sounds and the new engine for others. It's all one way or the other. If you were to "just stick on the ambience", then the new engine would be used for the ambience and you'd get no other sfx at all. Also a few of the fields have a stock ambience, so if you did import the vanilla sounds to the new engine, you'd have some fields with super high def ambience and some with crushed midi vanilla ambience. There are several areas in the game where doing this would be very awkward or be outright cringe. Some people suggest to change everything except battle sounds. The thing about that is many, many sounds are reused throughout the game. Just one example, a wave sound: The wave sound may be used in battle for the sewer monster, or Leviathan, but also used near the ocean. So, when you're near the ocean you'd suddenly hear midi waves next to HD sounds. This happens with probably half of the sounds in the game. There is also dealing with the complexities the mod adds like shuffled melee sounds. Setting up contingencies for if replaced battle sounds are off would compound those complexities. Which leads me to my second reason - I just don't want a hodgepodge mod where you'd have real recordings of birds etc. clashing against staticy-midi battle sounds. This was the problem with previous incomplete sfx mods for FF7. They only changed a hand full of battle sounds, which clashed against other battle sounds immediately surrounding them... Which leads me to most importantly; Cosmo Memory is a sfx replacement mod for the 724 vanilla sounds first and foremost. Identifying and making and editing and replacing them took 2 years to complete. That is the entire purpose of the mod - to update everything. The same way Nino replaces every model in the game, the same way SYW updates every field in the game, and the same way any music mod replaces every song in the game. The other features like ambience, footsteps, etc. were just last minute bells and whistles to go on top of them thrown in during the final couple weeks of development.
Most of the FF7 modder's philosophies are to provide the remake everyone really wanted. If Square had made the 1:1 remake, they wouldn't have used those original sounds...