Travis2544 :
Same company. It looks like msi also makes a gtx 970
Okay this is how it works. There are two gpu manufacturers: AMD and Nvidia
Nvidia and AMD gives sub vendors such as MSI, ASUS, Zotac, EVGA, Gigabyte etc their gpu chip blueprint/ architecture. The subvendors, in this case EVGA and Zotac, get the gpu blueprints/schematic/architecture and manufacture it. They put the card together and add they're own cooling unit to it.
In conclusion, subvendors such as EVGA, MSI, ASUS, Gigabyte are the ones that assembe it. They may not look the same, but they are all using the same GPU chip.
In your case, EVGA and Zotac are both using the same GTX 970 gpu chip. But the subvendors make different PCBs and add their own cooling unit. Sometimes, they may even overclock the chip. But at the end of the day, they are both GTX 970s.