Verticals have been used for many years in horizontal or even angled configurations. As per above, tell the manufacturer what you want to do and get his opinion. One of the main concerns would be when the pump is NOT running. If left for a long time at idle, the shaft could sag and develop permanent deformation.
Hydroturbines (pumps by night and electricity generating turbines by day)were laid angled up the sides of hills with no ill effects at all. I personally studied the effects of these with Herman Gruetink (an old vertical master) solely trying to find any deleterious effects from angle install. None were found.
Generally, I would say this is fine, but give us the details to tear apart.
length, stages, column length, shaft diameters, distance between lineshaft bearings, etc.