There's no disguise. Whoever this is just has a really bad hairdresser.
Nobody has interacted with Takuto yet, and you're leaving out one detail - if he is Paul's father and was a negative influence on him, Paul probably wouldn't talk to him.
Failing that, they could be saving the "oh my god it's Paul's dad" thing for a surprise twist when Ash finally faces him. This guy has to be someone notable, with the lengths they went to to conceal his identity until now.
Also, Paul is the only rival who hasn't even commented on him, which is highly suspicious to me. Barry (coincidentally, Paul's fanboy) saw Takuto up close, was horrified by him and then rushed off to tell his friends, while Conway knew about Takuto's accomplishments. Paul must know about him, so for Paul to know about such a powerful trainer yet not even drop a line like "I want to defeat you so I can fight Takuto," makes it seem like they are avoiding drawing a connection between the two for now.
Besides, Gliscor came back. All bets are off now, anything could happen.