Jeff Wu,
I use my nos tubed vk-5i with my vt100m2. It's one of my very favorite combinations. The warmth of the 5i goes well with the transparency of the vt100m2. It's almost like a vintage toned highly transparent system. I've heard more transparent systems, but this one seems to be 'just right'. I'm using audio physic avantis with these - the avanti's are so detailed that a warmer front end serves them well.
A friend who is a dealer brought over a vk50SE and a VK30SE on separate occasions and we hooked it up to the vt100. I used audio physic virgo speakers with vk30SE and vandersteen 5's with the 50SE. The vk30SE was much better than my pass labs aleph P with the vt100, and the 50SE demolished the ARC ref1 I was using with my vandersteen 5's at the time. It wasn't even close. Keep in mind that the vandersteen 5 is a little resolution starved, so ANY added transparency improves things. I do note that the aleph P was better with the aleph 2 monoblocks.
So, to answer your question, YES the BAT preamps are a good match for the vt100m2. I would say the 50SE is better than the 5i, but I note that I heard them 4 months apart, and with different cabling and speakers.