I agree with lfmn16, if you are playing originals well then you can play the songs anyway you write them. If you are playing slap covers with distinct slap lines then... ?
Really it deppends what the band wants from you, all of us have listened to enough funk artists to know that not only is slap bass not necessary for funk we could even name funk bands without bassists at all. But a lot of people who don't listen to much funk might expect you to play slap, and if you don't they may not want to hire you or play with you.
I wonder why you are so resistant to learn a bit of slap? I personally don't love slap either, it kind of throws your tone and mids out the window and makes everything sound like "clackity clack clack." For instance I much prefer Fleas tone when he isn't slapping. When he slaps it just sounds like loose tingy roundwounds snapping off a fretboard. Just my oppinion. But that being said, I can do enough of it to get by in certain sittuations if a song calls for it or is expected, and it's quite fun even if it's not my favorite tone.
Now about that George Porter Jr. video, I never saw him slap before either but I am even more suprised to see him playing through that Ampeg! When did this happen?