Short Answer: We believe they will.
We don't know which brand you're considering, and that sometimes makes a difference in fitment because not all tire manufacturers use the same method for measuring things (e.g., a width measurement for one company may be measured from one location on the tire to another. At another company, it may be measured from different locations on their own tire.) So even though two companies may show the same numbers on the sidewall, in reality, they may be significantly different in actual size. You can find some comments about this at tiresize.com's FAQ page.
The likelihood is that the tires you are considering in that size will fit in the wheel well. At the time of this writing (07/17/20), Our 1993 PUCH (G-Wagen) has Nitto Ridge Grapplers sized 35 inches in diameter by 11.5 inches wide. They're on 20 inch wheels that are 9.5 inches wide. See attached pics. This size of tire pushes the limit of what will fit in the wheel well for most any G-Wagen (AKA G-Class) from 1979 to 2017 since the body of the G-Class didn't really change much during that period, including the wheel well). So far, as of today's date, we don't have direct experience with the later model G-Class that changed significantly, so we won't hazard a guess about tire fitment for those trucks. We do, however note that yours is a 2014 G550, so yours is in the range of years where the fitment rule that I mentioned applies.
For a new set of 18 inch wheels that we will install on our truck, we will use 285/75R18 Nitto Ridge Grapplers. The nominal tire size you're considering is so much smaller than that, it has us believing that you should be fine to fit those tires with these AlphaEquipt wheels on your G-Class. Also, please know that the range of Nitto-approved rim widths for a tire with that nominal size is 7.5-9.5. The AlphaEquipt wheels have a 9-inch width.