Can you do upper body cardio or upper body weight training after laser vein removal for spider veins?

This mostly depends on the size of the veins treated. In general, I have no problem with this. If the veins were treated by ENDOVENOUS closure, then some abstinence from heavy weight bearing activity is needed. Endovenous closure is for varicose veins, not spider veins. This should be asked to your health care provider that provided the treatment, ideally.

There is no reason not to do any activities as the ones you mention after spider vein laser treatments. Read the ebooks and watch videos on my website. 

I do not recommend any restriction of exercise following topical laser treatment of spider veins.  I do recommend no hot baths or hot tubs for 48 hours and no sun tanning for at least 2 weeks.  For vein removal in the legs I do a procedure called microphlebectomy (2mm punctures) and I recommend support hose for 48 hours post treatment and resuming all kinds of exercise within 48 to 72 hours depending on discomfort and no swimming for 5 days.