Are the "h" in pinyin always pronounced as "[x]" in IPA?
Yes, h = [x] (also ㄏ in bopomofo).



Wikipedia has an entire chart entitled Help:IPA/Mandarin that lists consonants:


  


and vowels 


  




Many old dictionaries, especially topolectical dictionaries, used IPA or a simplified version of IPA.

Consider Li Rong's (李荣) edited Great Dictionary of Modern Chinese Dialects (现代汉语方言大词典). Here's an example from《哈尔滨方言词典》:


  


Here you can clearly see 火 is:


  xuo


You can also see that the other terms are also written using IPA, albeit slightly simplified.