Hello Sandeep,
That sounds like an interesting idea. I am not familiar enough with the WLAN RSSI to give a definitive answer, but CC2540 Bluetooth BLE device was specifically set up to avoid conflict with WiFi operating in that frequency range. With the CC2541, it may be possible since it does have a proprietary mode for the radio.
In theory, you could switch to proprietary mode, take your reading and the switch back to BLE. This you would have to do some searching on to see how flexible the WLAN radio you are using is. In the User Guide, there is a section that covers the radio for both devices.
You will have to compare the available modulation format of the WLAN to see if it has GSFK or MSK modulation which the CC2541 uses.
Thanks,