The VNH5180A-E is an automotive device, so it must withstand/survive test pulses at the supply line, which are defined in ISO 7637-2:2004(E), see the datasheet, pg 16. There is a built-in overvoltage clamp to fulfil these requirements.
So, it is not OK to run the VNH5180A-E permantely with 30V. The recommended operating conditions can be found in the datasheet pg. 9 under Electrical characteristics, giving for Vcc=5.5...18V.
Good luck!
/Peter
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