Im from Europa and I have never seen a Titan, RFA or whatever org from USA. I've seen WSOF cards though.
Any fighter would tell you he has more worldwide exposure fighting in WSOF than in Titan or other regional org, so it would be a step back for them.
About UFC/Bellator signing the top guys..not sure about that, maybe those who excite the mainstream fans. Im not sure about Bellator picking Branch or Okami and pay them what they worth to spoil their champion. It probably result on them fighting in Titan/One fighting even weaker competition than at WSOF now, or with even less exposure
UFC can pick whoever they want whenever they want, WSOF around or not