Hi,
The hci_app is indeed the application to use when you want to send HCI packets to the controller. What you are trying to do with the Wireless UART application is not applicable.
The Wireless UART application is (basically) an UART bridge over BLE. What you send to one KW41Z board via UART is forwarded to another board over a BLE connection and is written to the console (via UART).
If you want to embed some HCI code directly into the application, then you need some minor adjustments to your code. You are using Hcit_SendPacket which is the serial (UART) interface for sending HCI data. While this works for an HCI application, the Wireless UART application uses a full BLE stack (host and controller) so there is no need for a serial communication between layers. Try this:
#include "controller_interface.h"
hciPacketType_t packetType = (hciPacketType_t) 0x01;
uint16_t packetSize = 8;
uint8_t pPacket[8] = {0x14, 0x20, 0x05, 0x00, 0x00, 0xFF, 0x00, 0x00};
Controller_RecvPacket(packetType, pPacket, packetSize);