Is it safe to drink grain alcohol mixed with snake blood?
According to Biological risks associated with consumption of reptile products International Journal of Food Microbiology, Volume 134, Issue 3, 15 September 2009, Pages 163-175:
People are documented to have been infected with the following pathogens due to raw snake consumption:

Spirometra (Vietnam is specifically mentioned)
Gnathostoma doloresi
Pentastomids

See also Spirometra (Pseudophyllidea, Diphyllobothriidae) Severely Infecting Wild-Caught Snakes from Food Markets in Guangzhou and Shenzhen, Guangdong, China: Implications for Public Health The Scientific World Journal
Volume 2014, Article ID 874014:

In China, there are a lot of cases of human sparganosis caused by eating raw meat of snakes and frogs, drinking snake blood, and swallowing snake gall bladder [16]. Improper cooking methods of snakes will also increase the risk of infection, such as snake skin salad and halfcooked snake meat. In addition, Spirometra may contaminate tableware and food in the process of cooking snake meat. In the year of 2011, a patient suffered from bronchial sparganosis because he had a history of ingesting raw frogs, snakes, and drinking raw snake blood [17]. Another case of cerebral sparganosis reported in 2012 was caused by eating frogs and snakes [18]. In a separate report in 2003, all of the 11 patients infected by Spirometra had the habit of eating raw meat and skin of animals and 6 of them ate snake meat, blood, or snake gall [19]. In 104 cases from 2000 to 2006, 53.9% were caused by eating snakes or frogs [16].

...

More than half (55.0%) of the snakes were infected by Spirometra

Finally, concerning alcohol, see Effect of physicochemical factors on infectivity of Spirometra mansoni plerocercoid Zhongguo Ji Sheng Chong Xue Yu Ji Sheng Chong Bing Za Zhi. 2011 Oct;29(5):368-71 :

None of the mice fed with plerocercoids soaked in 60% ethanol for 2 h was infected. All the mice fed with plerocercoids soaked in 60% ethanol for 1 h, or in 50% ethanol for 2 h or 3 h were infected.

So even if the final concentration of alcohol after mixing was 60% (120 proof), and you wait 1 hour after mixing the blood and alcohol, it isn't necessarily sufficient to disinfect.