I was told the same thing about the heplock/salinelock, and after the trauma of my C/S, I just couldn't handle that. I still don't know what they put in that IV during my CS birth, or when, or why. Only that I had no say and no control over it, and my needs were completely overrun by what the nurses wanted to do. So to me, the IV/heplcok/salinething, it represented more than emergency access to my blood. It was me taking back control (and responsibility) for my healthcare decisions. So if you find yourself hung up on something, it may, like me, be not exactly about the something in particular but about your need to do different this round in general.
That said, I would find another option for a care provider. This one is not as enthused about your chances as they could be. We went through alot of providers before finding one who would get behind my decisions. It was a little scary because, once you take charge, you're repsonsible too, but it was so so so so so worth it. Worth the tirme to find her, worth the extra money, everything. I honestly was mentally prepared to even have another c-section, just as long as it was my educated, informed, responsible choice. But I got my VBAC, and odds are good that if you try, you'll succeed.
At my local hospitals, A VBAC mom has a higher chance (80%) of having a natural birth than a regular hospital patient without a previous C/S (64%).
My midwife group has the same statistics of C/S for VBAC mamas and all other mamas (3%).