HIGHLY variable depending on not only the country of training but the specialty you are anticipating practicing in.
General Surgery, for example, will allow some foreign training credit (this is relatively new) but the catch is you already have to be in a US training program to get the credit. You would likely not be hired or be given privileges without completing a US residency (and being BE/BC), although some exceptions are made for fellowship trained foreign surgeons or those who are recognized as international experts.
IMHO it is not "safe" to train abroad with the assumption that you'll be allowed to work in the US. Just read through SDN and see the sad stories of attendings from other countries working as phlebotomists, taxi drivers, etc.