i would not think that wood types would have any effect on the soulforge as that imbueing is checked vrs your skill and race. The only forge that has been mentioned to give a bonus is the queen's. I would however like to know if it changes the color of the forge as maybe a frostwood forge would look realy cool.....
I hit 95 imbuing on my crafter account and unraveled a runic piece that resulted in a relic. I was surprised and didn't even id it or make a note for a calculation check.
Anyway, I went ahead and unraveled a couple junk arties and got 3 relics. I made two out of three soulforges. The frostwood is UGLY like the ugliest thing I could put in my house. It is 4x4 and takes the entire center area of my tower. The developers basically just white washed every pixel.
My second one took two tries at 87.8% chance and I made a regular one to give to an old guildmate. He hasn't placed it so I haven't seen if it is as ugly.