Are you sure it originated from the Dum? Just a generally moist nose could be caused by him messing in his poo or drinking...
In any case if he's not already on newspaper.... I would put him on it... If the dum does hack up gunk (it happens sometimes) you'll see it better on newspaper... Dropping humidity slightly and raise temps is prudent but not too much... Mild
RI is best treated in my opion with a litle extra heat and normal humidity... No baytril needed...
Is the Dumeril's new? In a new cage? New setup? New location for cage?
RI doesn't magically appear; it's usually acts up do to stress or bad conditions.... Try to figure out whatever caused the problem in the first place and then remedy it as best you can. If the dum is in a high traffic zone move him away, etc.
As of now, it might be a false alarm. Watch him closely and then work from there...
Good luck....