I researched this on other forums when BF4 first came out. The consensus on those forums is that BF4 is 64-bit and Sonic Radar is still 32-bit. I'm not sure how the overlay functionality works itself, but I do know that on Windows, 64-bit and 32-bit cannot communicate directly. They are isolated memory spaces. Which is why Microsoft still recommends using the 32-bit version of Office just in case you rely on a 32-bit compile plug-in.
In my job, I needed a web app running on a 64-bit JVM to communicate with a 32-bit Windows dll. I had to write a Java web service and run it on a 32-bit jvm as a bridge. The 64-bit jvm app calls the web service on the 32-bit jvm that then calls the 32-bit dll.
My guess would be that Sonic Radar would need to be compiled as 64-bit and all would work fine; however, there maybe other internal considerations that may make that compilation not so simply.
MonkeyForce9
a.k.a. "DoGood"
Intel Core i7-4770K @ 4.4GHz * Corsair H100i Water Cooler
Asus Maximus VI Hero * G.SKILL Trident X 16GB DDR3 2400
EVGA GTX 780 Ti Dual Classified 3GB Video Card x2 SLI
ASUS PB278Q 27" 1440p Monitor @ 80Hz
Samsung 840 EVO 500GB SSD * Asus Blu-Ray Burner
Cooler Master Silent Pro Gold 1000W PSU * Corsair Obsidian 550D Black Case
Corsair Vengeance K70 Cherry MX Red Keyboard * Razer Naga Molten Mouse
Razer Tartarus Keypad * SteelSeries Siberia V2 Headset