Mostly no, but in some cases it's worth trying the combination to see if your hair like it. BUT it depends on which silicone we're talking about. In general, silicon is the strongest smoothening + moisture retention agent you can find, so if you use it, your hair should already be quite fine with it as sealant on its own. If you use a friendly/airy silicone that can be removed by oils, then no, you shouldn't combine them. Because the oil you'll apply will dissolve the silicone coating which kills the purpose of it. If you want to use a resilient silicone that won't be removed by oils, then you should apply your oil sealant BEFORE your silicone. Otherwise the oil will simply sit on top of the silicone and not even benefit your hair (and maybe even make it look greasy).