Yeah both can be equipped at the same time, but note you do need to own the regular textures for Bumpmaps to work.
As Sly said they basically add 3D depth to a texture set but currently have some technical issues.
That being, when the option is turned, on all the textures will turn a shade of grey. But, i hope and bet this will be fixed in the final release of 3.9, if not 4.0.
Thorn: ray fucking join like what the fuck are you doing you fucking cunt bitch
Thorn: you little shit
Thorn: fuck your shit bitch
Thorn: eat a dick
Thorn: I'll fucking lynch your shit