Are there any complications due to Botox being injected into a vein that I should be concerned about?

If significant amounts of botox is injected into a vein, other problems would occur with breathing, etc. Otherwise, 'hitting a vein' can cause more bruising than usual but nothing more than that. 

When an injector hits a vessel when injecting Botox, you would likely have a bruise for a short while. Beyond that, no complications are anticipated from the Botox reaching the blood stream due to the very small amounts usually injected. The bruise should settle down within a few days. Good luck!