Huascar - GEX and UTX should not cause any issues because they do two different things. GEX does ground textures, scenery and autogen objects (repetitive trees, houses, buildings land usage). UTX does scenery - rivers, streams, roads, railways, bridges etc...
So if you have issues, you may not be installing them correctly - especially if you have some Land class (mesh) files that do topography (hills, mountains, valleys and plateaus) like FS Genesis.
The correct sequence is 1. Land Class - Mesh files (FS Genesis, FS Global X 2010, etc) 2. Ground Textures (FSscene, GEX, etc) and 3. Scenery (UTX). Note: I have GEX US and Europe and FSscence World so here is my install sequence:
3. GEX (this is next because I want to over write North America and Europe FSscene areas with GEX US/Canada and Europe)
4. UTX USA (this is last because I want the roads, bridges, etc - over the GEX US textures)