IC which can drive an RGB input to two outputs
VGA means you have a 75 Ohm source on each RGB signal that is ~1Vpp when loaded by a 75 Ohm load (monitor)

Loading with 1/2 * 75 Ohms implies you need the same source impedance to get the same voltage. for black and white levels.

It will work but only only at 50%luminance. (peak voltage =100% bright)

Then you can compensate on monitor or leave as is.

When you use long coax cables, if you have 75/2 Ohm load and source now any mismatch may result in ghosted edges with cable being 75 Ohms.

A video splitter amp uses separate 75 Ohm video buffers for each output to drive monitors directly near DC to xxx MHz .... unlike RF splitters which use hybrid transformers.

Here's a collection of suitable designs from LTI
http://cds.linear.com/docs/en/application-note/an57fa.pdf