Apparently there were studies on adenovirus 5 vector vaccines against HIV in 2007. The vaccine was not successful, but I cannot find any data on long-term adverse effects.
Plenty of replication deficient things cause cancer, for example asbestos or igf-1. I highly doubt you can rule out accidental crosstalk between elicited immune antibodies and every oncogenic human receptor.
How many genetically engineered adenovirus vaccines have there been before?
The vaccines that are your prior are typically attenuated or inactivated virus.
Majorly different category, we are in untreaded space (I'm still planning on getting one)