I wouldn't buy an IGH for a vertical dropout bike and assume you'll be fine without a chain tensioner. There are some possible solutions: magic gear, Phil EBB, half links, but I have come across more than one unhappy rider who tried those solutions. If you can live with a chain tensioner go for it. You can always try and get rid of it and if you aren't happy you know you'll have a solution you are okay with.

I was able to setup my BF NWT with a Surly tensioner in push up mode [image above] - which kept the clean IGH chainline and worked with my vertical dropouts.