Can pathogens enter the bloodstream if the epidermis has been scraped off?
Our epidermis is the first line defence against natural infections; it is also a part of the innate immune system. This is due to 


it contains a layer of dead cells that separates the living cells of the deeper layers of epidermis and dermis from the environment.
This part of the epidermis is avascular and so pathogens can not easily enter into the bloodstream through it. 
It contains natural bacterial flora (like in our gut) that kills a large number of pathogenic microorganisms with their toxins. 
secretion of sebaceous gland contains some antimicrobial substances. 


There are lots of other protective features of epidermis. 

Dermis is richly supplied by blood vessels. So even if all the layers of dermis remain intact its high vascular nature will act as an open entrance of microorganisms. By definition abrasion involves only the epidermis or some parts of the dermis but still we need to take tetanus vaccine after getting an injury contaminated with soil. In diseases like Stevens-Johnson Syndrome (where epidermis separates from dermis) or in burn patients the skin is covered with antibiotics and dressings. The patient is also given high dose of antibiotics to fight those bacteria that still entered into the bloodstream.