You're about five to six or more years from applying for a Vascular Surger fellowship, so it's sort of difficult to say how competitive they will be.
Vascular Surgery has sort of come around in the last few years with more interest amongst General Surgery residents and, therefore, more competition. The match rate for Vascular Surgery has fallen to just above 80% in the 2007 Match (the one I was in), from just above 85% the year before. So all indications are that the current match, to take place next month, it'll probably be about the same or slightly under 80%.
As a profession Vascular Surgery is set to expand thje number of training opportunities. The larger centers have already established integrated 0+5 programs matching fourth year medical students. Very likely we'll be seeing more large centers establish similar programs in years to come. There is currently one 3+3 program at Rochester. There currenty aren't any 4+2 programs. I'm not sure what all this love for the integrated or ESP (Early Specialization Programs, referring to the 3+3 and 4+2 models) is going to mean for traditionally trained 5+2 fellowships. Will they go away? Will they freeze these numbers and increase the number of integrated and ESP positions? Only Nostradamus will know. So keep this in the back of your mind if you're sure Vascualr Surgery is what you want. I say this because while you may think you like Vascular Surgery today, or General Surgery for that matter, you may not like it by the time you become a fourth year General Surgery resident set for the Vascular Surgery match.
Anyway, currently matching into a Vascular Surgery fellowship is not impossible. It's certainly more difficult than Trauma, MIS, CVTS, and a few other surgical fellowships/residencies, but so long as you have decent ABSITE scores, good LORs, and interview well enough you'll get a spot.
Now where you match is really the question. The most competitive positions are highly competitive and usually require quite a bit of research or papers published.
I'm a community program Chief Residdent with solid ABSITEs, at least several papers and presentations (not all Vascular Surgery), and excellent LORs and I received plenty of interviews, some of which were at top fight programs.
Anyway if you have other questions, don't hesitate to ask here or PM me.
Good luck.