Arduino ESP8266 Ticker interrupted by DallasTemperature/OneWire?
Ticker does not interrupt your code. It is a OS-timer and will call your function once the time is elapsed.

The Tiker callback can be interrupted by a "real" interrupt or another Task with higher priority and does not provide any reliability - it will just be called. 

A solution (not the best) would be to disable manually all interrupts, if you can't solve it in another way.

If you just want a blinking led, you should use a Timer interrupt as your callback is short and fast. Maybe with the ICACHE_RAM_ATTR attribute.