Can I wear a navy warfare pin on my ACU/ASU?

There's nothing more sure than a regulation. Read the regulations, you need to be familiar with referencing them in order to be an effective leader in the Army. If you have questions about what you read, then ask again here.

AR 670-1:
22-12g(3): In accordance with AR 600–8–22, personnel must obtain written authority from Army Human Resources Command, Awards and Decorations Branch, before wearing badges on the uniform that were awarded by other U.S. Services or by the Director of Civilian Marksmanship. The following rules apply when wearing badges from other U.S. Services:

Badges from other U.S. Services that indicate career fields are not authorized for wear (such as U.S. Air Force medical insignia or badges used to identify the duty, function, or classification of the wearer). Some examples are U.S. Air Force fire protection, air training command instructor, security police, or Naval Qualification Badges such as the Naval aviation warfare specialist.

Meaning: Authorized only if you have written permission from Army HRC (A&D).

The regulations vary from branch to branch. Typically, if you take the time as Army to earn a Navy Warfare insignia, it's done as an extra military function. This would be akin to a Sailor TDY with an Infantry unit, meeting the qualifications for CIB except for actually being in the correct career field, then having a commander approve it as an honorary badge. The award is outside official channels and almost always doesn't have a place of official placement.

That doesn't mean you can't wear it, but rules apply. For the Air Force, there are 13 classes of badges, the higher ones being aviation. Aviation badges earned in other branches may be worn, but foreign aviation badges can only be worn while serving in or with the nation that issued it. Other badges, such as SCUBA, if earned elsewhere, can only be worn if serving in a SCUBA career field. What's odd, is my Navy Enlisted Warfare is roughly coequal with all other warfare badges, which includes Aviation, Astronaut, Submarine, SEALS, Surface and enlisted equivalents. But the Air Force singles out any Aviation Warfare and you can wear it in a higher rank position, but allowed me to wear my Surface Warfare with the lowest rank. Since I only had a duty badge and Surface Warfare, I wore them both. Had I taken the time to get my Aviation Warfare, I could have worn it in the primary position.

Most branches limit you to two such badges on the dress uniform. For Navy folks, it is possible to earn multiple warfare badges and have additional permanent badges in the warfare locations, such as Aircrew, Submarine Deterrant Patrol or various Small Craft Coxwain badges. You can only wear 2. Three or more warfare badges means the primary is based on your command, you may pick the 2nd. So having both Surface and Aviation warfare can change if you're on a ship or air station. If you also have Submarine, you can get creative and wear whatever 2nd one you want. The other special qualification badges are still official, but if their not in the top 2, don't wear them.

The Army tends to allow you to clutter your uniform with badges. Since many are smaller by design to allow them to be worn side-by-side with your ribbons, I think there's room for 4, plus a Combat badge if earned. Each branch also has additional rules about what badges go on pockets, pocket flaps, or some other position.

The short answer is just because you earned it doesn't mean you can wear it, and if you can wear it, it doesn't mean you get to wear it how you think it should.