I don't think you're describing alt-right employees, I think you're describing Republican employees. The standard position of the Republican party since well before Trump was that Cops are great and protesting is bad (especially when it is "thugs" "rioting"). During the Bell Curve, the standard Republican position was that the book was both scientifically accurate and useful for determining social policy. Jesse Helms existed. Since BLM, the standard Republican position has been "Blue Lives Matter and All Lives Matter". The Republican party has been, since the 1960s, racially conservative. And since at least the 1980s the Republican party has been against what they perceive as the excesses of modern feminism, and "political correctness". If you check public opinion polls on cops/BLM/protests against police brutality, you will see how it basically 1:1 lines up with race and party. And if the question is "I find Republican views abhorrent, how do I make my employees not be Republican?" I think you will probably find that's a losing battle.
I think it's important to keep some daylight between the Republican Party and the alt-right because, first off, the former is large and the latter is small and I think it's actually possible to combat the latter; second, because the willingness to use apocalyptic language to refer to your opponents means you have nowhere to go when the real apocalypse comes along. By that I mean that many Republicans wrote off criticisms of Trump as unqualified, extreme, or unsuitable for office because those same criticisms were made against Romney and McCain and Bush and Dole and Bush and Reagan and... Not necessarily to the same degree of course, but an acknowledgement that there are different degrees and reserving the harshest criticism for the worst abuses is an important part of the arguments sounding credible to moderates on the other side.
If your employees "ironically" dress up as Nazis, spam pepes, write "The God Emperor is Going To Gas You" on a Jewish employee's locker, talk constantly about race realism and race traitors and a white country, say openly racist things about the appearance of others, etc. then you are in a space where it's both easier for you to take action and more accurate to characterize them as alt-right. And the answer with how to deal with someone doing this kind of stuff is to summarily fire them. Abuse and harassment in the workplace can't be tolerated at all.