BLE was specifically designed to co-exist well, so no need to worry here (:
For a more visual explanation, this page has a very nice illustration:
http://www.argenox.com/a-ble-advertising-primer/
Note how the BLE advertisement channels (i.e., the ones that beacon broadcasting uses) are positioned between the WiFi channels, and also spread out quite a bit, so that even if there’s a microwave introducing lots of noise on one end of the spectrum 
, the other should work fine.
RSSI is usually more affected by environmental factors—radio waves bouncing off of objects, or being blocked by them, etc.