I have 3 Jacobs Ladders on right next to each other and haven't had a new one show up in awhile. It's just sometimes you get them and sometimes you don't. Oh, and you have to have a perfect town, if you didn't know that.
I don't think so. I do know people plant Jacob's Ladders near flowers they're trying to hybridise as a way of controlling what might bloom. It's because unlike other flowers, you can't get more by watering them.
Since nearly nobody seems to understand what you mean, here is my answer: I've never tried placing one next to a breeding pair, but I did read on a wiki that it increases the chance of flowers growing (a bit in the way of fertilizer). I've also seen people on the forum do this, and I suppose they did it because it worked. That's actually how I found out about this trick.
I believe so, whenever I try to breed flowers I place them horizontally next to each other, and then I place a Jacob's Ladder on each side. It seems to work well for me, and better than before I used this method.