Not sure what you have your country,Plumber merchant should have them,they come in about 3/4" wide and peel off both side and the right thickness for bedding down the hob onto the worktop or you can get rubber foam tape type material.
You can,but it would have to be heat proof and if the hob have a slight twist it will start rocking where putty tape with 3mm thickness hold it better.Silicone sealant is really for filling gaps and some manufacter's don't recommended it.
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