It's still weird for me to see Clark and Oliver like this on Smallville for two reasons:

1. It seems like they're just doing the Clark Kent/Bruce Wayne dynamic and replacing Bruce with Oliver. Clark and Oliver were acquaintances and Justice League teammates in the comics, but they were never close friends, as Clark operated on the east coast with Bruce while Oliver was based on the west coast with Hal Jordan.

2. In Frank Miller's The Dark Knight Rises, Oliver appears to hold an old grudge against Clark and implies that something bad may or may not have happened between them.

When Bruce asks Oliver what he wants, Oliver replies, "I always knew it'd get down to you and the big blue schoolboy. Planet's too big for the two of you. When it all comes down... I want a piece of him. A small piece will do. For old times sake." And then Oliver points to his missing right arm and says, "You know... it still hurts when it's cold..."