Rebuilt RtlAddVectoredExceptionHandler so that it doesn't use the ntdll imported function. This way it would be more difficult than just putting a breakpoint on RtlAddVectoredExceptionHandler to log your function. To make it a little better you could inline EncodePointer which would only a few extra lines. Structs might be documented somewhere h…

AddVectoredExceptionHandler.cpp

#include <Windows.h>
#include <winternl.h>

// Types
using LdrProtectMrdata_t = void(__stdcall*)(int);
using LdrProtectMrdataHeap_t = void(__thiscall*)(int);

struct ExceptionRecord_t {
  LIST_ENTRY entry;
  int* unknown_intptr;
  int unknown_int;
  void* handler_fn;
};

struct Handler_t {
  PSRWLOCK lock;
  LIST_ENTRY entry;
};

// Functions
void* NtAllocateHeap(size_t nSize) {
  return HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, nSize);
}

void AddExceptionHandlerRebuilt(void* pVeh) {
  Handler_t* LdrpVectorHandlerList = *(Handler_t**)(PatternScan(g_hNtdll, "81 C3 ? ? ? ? 8D 7B 04") + 2);
  LdrProtectMrdata_t LdrProtectMrdata = PatternScan<LdrProtectMrdata_t>(g_hNtdll, "8B FF 55 8B EC 51 56 57 BF ? ? ? ? 57");
  LdrProtectMrdataHeap_t LdrProtectMrdataHeap = PatternScan<LdrProtectMrdataHeap_t>(g_hNtdll, "8B FF 53 56 57 8B F9 E8 ? ? ? ?");

  ExceptionRecord_t* pNewRecord = (ExceptionRecord_t*)NtAllocateHeap(sizeof(ExceptionRecord_t));

  pNewRecord->unknown_intptr = (int*)NtAllocateHeap(sizeof(int));
  *pNewRecord->unknown_intptr = 1;

  pNewRecord->handler_fn = EncodePointer(pVeh);

  Handler_t* pHandler = &LdrpVectorHandlerList[0];
  LIST_ENTRY* pEntry = &pHandler->entry;

  LdrProtectMrdataHeap(0);
  LdrProtectMrdata(0);
  AcquireSRWLockExclusive(pHandler->lock);
  
  if (pEntry->Flink == pEntry)
    _interlockedbittestandset((volatile LONG*)(__readfsdword(0x30) + 0x28), 2);

  if (pEntry->Flink->Blink == pEntry) {
    pNewRecord->entry.Flink = pEntry->Flink;
    pNewRecord->entry.Blink = pEntry;

    pEntry->Flink->Blink = &pNewRecord->entry;
    pEntry->Flink = &pNewRecord->entry;
  }

  ReleaseSRWLockExclusive(pHandler->lock);
  LdrProtectMrdata(1);
  LdrProtectMrdataHeap(1);
}