Pete's and Gian's comments thirded! There would be no reason for a specific engineer unit in Pavis given that this is essentially static garrison work in a well-built area or else roving patrols, neither of which requires major construction. Remember that units are used to being in the field and will have a degree of natural experience, just as - as Gian notes - they can hire local expertise.
That said, there are various specialised cults and herocults within the Imperial Army catering for particular expertises. This is noncanonical, but I roughed out Ettal Vorn the Siegemaster as a YT subcult some time back. If anything, an engineer might be a subcult/herocult of IO (knowledge put to practical use) or even Lodril (for the Yelmics).
All the best
Mark
Mark Galeotti
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