Does a buyer have any exposure to disputes over surplus proceeds after a municipal tax sale?

Generally, no - a buyer's role in this part of the process is limited, and disputes over any surplus are typically a separate matter between the municipality and the parties who had an interest in the property, not the purchaser. If a tax sale generates proceeds beyond the cancellation price and the municipality's costs, that surplus is generally held and made available to the former owner and any other parties with a registered interest, such as a mortgagee, through their own claims process against the municipality.

Once you have completed your purchase and paid the accepted tender price, your involvement in the transaction is essentially finished from that point forward; you are not a party to, and generally have no financial stake in, how any surplus gets distributed among competing claimants afterward. This is one respect in which a tax sale purchase is relatively clean for the buyer, compared with some of the other risks - occupancy, condition, and title nuances - that do fall on your side of the transaction.

If you have specific concerns about surplus proceeds in a given sale, ask your lawyer to confirm how that particular municipality's process works, since practices can vary.