How likely is it that hbp meds contribute to spider veins since the meds function is to open blood flow?

Not at all likely: There are many types of high BP meds that work in a variety of ways. Some affect arteries, some affect veins, and some affect both. All work to reduce pressure in the vascular system. Spider veins are very small veins that are caused by too much pressure in the venous system, not too little.

No link: Spider veins usually occur because of poor valve function within the veins, and subsequent backflow to the superficial veins. Meds for arterial bloodflow typically don't make a difference to this.