RadioHead and DallasTemperature error
I have experienced many issues when using RadioHead library on ATTiny85 together with the Arduino IDE. Your issue is not the Dallas temp sensor.

The problem lies in that RadioHead uses timer 0 on the ATTiny and changes the prescaler on the timer to match the baudrate you have requested for your tranciever. The change of prescaler changes the way Arduino IDE functions like delay()works since those also use timer 0. I believe your Dallas library depends on delay() to synchronize the signals on the 1-bus so there you have a conflict between the two libraries.

I solved this by rewriting the RadioHead RHASK files to allow for ATTiny85 timer 1 to be used instead. Here's my code. Although I use TinyHead instead of RadioHead, the change will be the same as TinyHead is a RadioHead clone.

The only change I made to RH_ASK.h is the code to define whether to use TIMER1 or not.

// Flag to indicate whether to use timer1 in attiny85.
#define RH_ASK_ATTINY_USE_TIMER1


The below changes goes into RH_ASK.cpp

First change. Update pre-scaler code and add the pre-scalers used by timer 1:

// Put these prescaler structs in PROGMEM, not on the stack
#if (RH_PLATFORM == RH_PLATFORM_ARDUINO) || (RH_PLATFORM == RH_PLATFORM_GENERIC_AVR8)
#if defined(RH_ASK_ARDUINO_USE_TIMER2)
// Timer 2 has different prescalers
PROGMEM static const uint16_t prescalers[] = {0, 1, 8, 32, 64, 128, 256, 3333}; 
#else
  #if defined(RH_ASK_ATTINY_USE_TIMER1)
   PROGMEM static const uint16_t prescalers[] = {0, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16834, 3333}; 
  #else
   PROGMEM static const uint16_t prescalers[] = {0, 1, 8, 64, 256, 1024, 3333}; 
  #endif
#endif


Second change. This code sets up the timer 1 and goes before the existing code for ATTINY timer0 in function RH_ASK::timerSetup(). please note the "... existing code" part. The existing code for setting up timer 0 goes between the #else and the #endif

#if defined(RH_ASK_ATTINY_USE_TIMER1)
#warning RH_ASK_ATTINY_USE_TIMER1 set.
   // figure out prescaler value and counter match value
   // REVISIT: does not correctly handle 1MHz clock speeds, only works with 8MHz clocks
   // At 1MHz clock, get 1/8 of the expected baud rate
   prescaler = timerCalc(_speed, (uint8_t)-1, &amp;nticks);
   if (!prescaler)
       return; // fault

   TCCR1 = 0; // Stop the timer
   TCNT1 = 0; // Zero the timer
   GTCCR = _BV(PSR1);  // Reset the prescaler

   // Number of ticks to count before firing interrupt
   OCR1A = uint8_t(nticks);

   TCCR1 = _BV(CTC1); // Turn on CTC mode / Output Compare pins disconnected

   // convert prescaler index to TCCRnB prescaler bits CS00, CS01, CS02
   TCCR1 |= prescaler; // set CS00, CS01, CS02 (other bits not needed)



   // Set mask to fire interrupt when OCIE1A bit is set in TMSK
  #ifdef TIMSK0
   // ATtiny84
   TIMSK1 |= _BV(OCIE1A);
  #else
   // ATtiny85
   TIMSK |= _BV(OCIE1A);
  #endif
#else
#warning RH_ASK_ATTINY_USE_TIMER1 not set.
   // use timer 0 (default)
   // figure out prescaler value and counter match value
   // REVISIT: does not correctly handle 1MHz clock speeds, only works with 8MHz clocks
   // At 1MHz clock, get 1/8 of the expected baud rate
   prescaler = timerCalc(_speed, (uint8_t)-1, &amp;nticks);

... existing code

   // ATtiny85
   TIMSK |= _BV(OCIE0A);
  #endif
#endif


Third change goes where the vectors are set up. Note the added #if defined for TIMER1 and the corresponding vector. Note also that the vector for timer0 is now called TIM0_COMPA_vect in later RadioHead/TinyHead but the names TIMx and TIMERx are interchangeable.

#if (RH_PLATFORM == RH_PLATFORM_ARDUINO) 
#if defined(RH_PLATFORM_ATTINY)
 #if defined(RH_ASK_ATTINY_USE_TIMER1)
  #define RH_ASK_TIMER_VECTOR TIMER1_COMPA_vect
 #else
  #define RH_ASK_TIMER_VECTOR TIMER0_COMPA_vect
 #endif
#else // Assume Arduino Uno (328p or similar)


Mind you that I have had other issues using the DallasTempSensor library. I'm not sure whether the issue is a low quality crystal in my ATTiny or not, but I get garbage readings from my sensor. The same code works flawlessly on my Arduino Nano, so I'm currently investigating whether my ATTiny is too far off in its timings to work properly with that library. I'm also going to try the OneWire protocol to see whether that one works better. However, the above code change resolved my issues with Arduino IDE and RadioHead/TinyHead.