We have a case where Orks were infested with Nurgle's... something, and
became sacks full of nurgling eggs. Xenos (non-human species) are susceptible to Nurgle's influences on different levels. Although there does seem to be a distinct lack of Nurgle fluff on non-human species.
As for melee units, for example, in the
HH novels the Space Marines who encountered Daemons of Nurlge don't usually get infected unless their armors were cracked open or their helmets blew away. Therefore in an isolated battlesuit, Nurlge's diseases can have a hard time penetrating.
Another example is from the new, eh, Tempestus Scions codex, Tempestor Brellius of the 68th Deltic Lions was infected with some Nurglite AIDS or some thing because a
Great Unclean One vomited on him after breaking his mask. Note that the planet they are fighting on is "no more than a hundred miles in circumference", which means the density of that planet must be extremely high, why anyone would live there is anybody's guess. But I digress. Anyways as long as a soldier don't get into physical contact with infection sources, they will likely be fine. And if they do get infected, they get executed, no doubt.
Also Nurgle's disease don't infect equipments instantly. They warp the shapes and probably abilities of those equipments slowly, usually because they are very close the infection source for a very long time (like the armors and weapons Death Guards carry), they can be salvaged by the usual sterilization methods, post battle.
Lastly, it is often said that a Daemonic Incursion usually involves some form of post-battle culling. Taints are to be sort out and removed, and the minds of those more valuable are wiped. So every Daemonic Incursion is a great event where quarantines are to be set up and huge amount of lives lost, which would make sending countless warriors to death even easier. I'd assume for the specialized fighting forces like the
SM, SOB and
TS, their infected will first be isolated, probably treated. Those who cannot be saved or not worth risk saving are granted "The Emperor's Mercy", their equipments incinerated and infected medical devices, including medicea servitors are shot into a dying sun or something. Kind like how to deal with highly infectious diseases now, 'cept for the dying sun. Just wear protection gears and hope for the best.