We recommend the following to connect the devices.
VE-500
Connect your guitar to the INST input of the VE-500 and the THRU output next to it to the input of the GT-001, through which you can send the dry guitar tone to the GT-001. This way, you can send the vocal tone from the VE-500 and the guitar tone from the GT-001 to a multichannel amp or mixer.
VE-8
Plug your guitar into the VE-8 guitar input. The VE-8's LINE OUTPUT jack and XLR connectors are configurable to output what you want. For example, the XLR output can be used for vocals and the line output can be used for guitar tone, so you can connect the L/MONO signal to the GT-001 input, for example. You can then send the output of the VE-8 and GT-001 separately to a mixer or multichannel amp.
It is not recommended to send the effected guitar signal of a GT-001 to the VE-500 or VE-8, because the chord recognition works better with dry guitar sound.