Yes, that is exactly how many native speakers pronounce this word. If we are enunciating the word extremely carefully, we would say /ˈɪnpʊt/.  However, in natural speech, even at slow speed, the bilabial /p/ may affect the quality of the previous consonant, so the word would be pronounced /ˈɪmpʊt/. This change is quite natural and common, and has even impacted on the language. This is why the opposite of 'possible' is 'impossible', and the opposite of 'mature' is immature'.