As I understand it that would only happen on a 1 (DC20 on a d20+10 roll so max failure is 9). Otherwise it just fails to come into being or you have a 30hd dragon on your side.
For conjuration I am thinking about a DC increase. Alternatively many of the potential issues, like a basilisk being summoned at mid-levels, can be eliminated if the PC and DM work together to come up with a reasonable summon monster style list of creatures before hand. IMC this would be necessary also as the summoner is required to have the monster stats printed out and on hand, not from the DM's MM, to use the creature.
For conjuration I am thinking about a DC increase. Alternatively many of the potential issues, like a basilisk being summoned at mid-levels, can be eliminated if the PC and DM work together to come up with a reasonable summon monster style list of creatures before hand. IMC this would be necessary also as the summoner is required to have the monster stats printed out and on hand, not from the DM's MM, to use the creature.