This post is a little old now, but I'm reviving it as I am experiencing similar issues with render performance (Vray 3.3). I'm using Max's Vector Map to mask large areas via a Composite map.
In all other configurations of the material not involving the Vector map, I found rendering to be much quicker. I've played around with various settings in the Vector Map texture, but to no particular advantage unfortunately.
Oct 24, 2018 - - Construction Colors, Materials, and Design. - Wireless and Other Telecommunication Facilities. This only happens in the viewport with the right settings but does not carry over into the final render, to use an image texture in the final render you need to setup your material properly.
Bitmap Texture Of Material Not Showing In Render (toucan)
The work around Vlado has suggested above doesn't make a difference in my particular scenario, likely because it's not related to GI since it's only being used for masking purposes. If there are any updates on this since 2014, or anyone else has some tips I could try, I'd be very keen to hear about it since render times around 500% longer than without vector maps. Ideally I want to avoid converting to bitmaps, but if that's what must be done, then so be it. When the vector map was released I thought that times with vector masks where finally over. Unfortunately I found out that using vector masks was slowing down so much it would literally not be possible to use it in production. Since then I asked Vlado to create a VrayMap that could work based on projected splines but I never had any response.
In the mean time / as a work around, you could use the VrayDistanceTex. This is what I use ATM but hopefully Vlado will hear our needs about vectored maps Stan.