Any of the ancistrus and hypancistrus would do fine up to about pH 8 but if your tank is higher pH than 8 I wouldn't recommend adding them.
Also I have mixed synodontis cats with ancistrus without any problems. I have never mixed hypancistrus with syno. cats. My guess is that they would coexist okay as long as you had some wood, rockwork or pleco caves for the hypancistrus to claim and reside in.
Ron