The company's Facebook account only appeared on May 1st and their Twitter sometime since then [1][2]. It also appears that their website only became public on May 4th [3]. Given the recentness of their public presence, I would not imagine that they were expecting this much publicity yet.

I think that they are legitimate because the "What's Inside" photo for the Nikola One is definitely an export from a real CAD model [4]. And Google Image search cannot find the photos they have on their social media profiles used anywhere else besides when referring to them [5]. That said, they seem distinctly in the prototype phase and have a long way to go before actually shipping something. Tesla took 6 years to ship less than 150 cars. [6]

[1] https://twitter.com/nikolamotor

[2] https://www.facebook.com/nikolamotorcompany

[3] http://whois.domaintools.com/nikolamotor.com

[4] https://nikolamotor.com/one#safety (my dad does mechanical engineering, and the only place I've seen pictures like the one on Nikola's page is in CAD exports)

[5] (monster URL, had to shorten) http://tinyurl.com/zsvt8hx

[6] https://en.wikipedia.org/wiki/Tesla_Motors#History