Hey @MFrankJohnson,
When you change providers any data that ISP’s (inbox providers) have on you associated with your domain will not change. However, ISP’s also keep sending reputation data associated with IP address and that will be subject to change.
Different ESP’s can track opens differently. It mostly comes down to how/if you look for bots. HubSpot will filter out engagement that is clearly from a robot. I do not know if, or how, Vertical Response open tracking may work differently.