Yes and no. If you specifically want the specularity then you will be okay (as it says on the download page). I'll give the full description for the future reference of other people, though.
If you want (for example) the Grimjaw Ork Warboss skin with the fluffy Orks then you can just copy the Orks in and then paste in the Warboss. That'll will overwrite the fluffy Warboss and you'll see fluffy everything *except* the Warboss.
If you want to merge two textures then you'll need to follow
Skinning 4 Dummies and manually edit the textures so that you get the features you want from each in a single file, creating your own hybrid texture set. The success rate there depends on what you want to do.
The specularity effect is a special case, though. Team colouring was done in WTP files, but Specularity is done in the RSH file (a base file for effects and the default colours). That means you can have both by simply copying all the RSH and WTP files you want into the right folders.
Hope that helps.