Can we report scamming attempts here?

tl;dr version: There are exceptions to calling out, the calling out in question may not in fact be against current site rules, and banning is never directly related to calling out.

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to call out any account

Exceptions (at least in the past; It's always best to first confirm current rule exceptions with staff before engaging in them):
If it's not a real user and you have clear evidence of such (ie, you're allowed to reference if someone is imitating your account), or if you're referencing it within the scope of a public identity (eg, referencing curators or developers, specifically in their role as curators or developers, rather than as users), or if the account owner brings up the topic first within the same discussion or intentionally presents it within a "public" location.

To clarify that latter point, it's (by past precedence) fair game to reference posted information on someone's Steam profile, as they deliberately set that up themselves, but not okay to negatively reference someone's ratio or other Steam stats as those occured secondary to other user actions [ie, they have control over the underlying actions but not the displayed information], or to reference other threads/websites as they're not presented publicly relative to the given thread. That's a tight enough distinction it's generally best not to go poking at it unless there's a clear reason to do so.

Finally, the information presented actually has to be negative (either by intent or by likely community interpretation), given the rule such policies were based on [ie, you can't call someone* out for being too awesome, support won't take that seriously]. That all said, that's all based on the previous site rule (which was along the lines of "if you have an issue with another user, report it to staff rather than engaging that user about the topic"), which no longer seems to be present within the current site rules. The current relevant site rules actually have some exceptions as far as calling out, and are much more specific on what constitutes calling out:

If you notice a user not following our guidelines, do your best to politely explain our rules with relevant links or quotes to our guidelines when appropriate. If they do not take action or deny any wrongdoing, please submit a user report ticket so we can take action if necessary.

To remain respectful to giveaway creators, do not write comments that question the legitimacy of their giveaways. For example, it would be inappropriate to comment that a giveaway is "fake" when you notice a new user has created a giveaway for a highly desirable game.

[No] Personal attacks or hate speech. Threats, harassment, and slurs (e.g. insults towards a user's race, sexual orientation, or gender) are not allowed.

You should always refrain from writing comments which accuse users of posting fake giveaways, or question their integrity.

I may be overlooking it, but I don't actually see any general rule against calling out anymore, within the current site rules. So while it may invite punishment, it (assuming I didn't overlook the relevant section) doesn't actually seem to be against site rules anymore. This is true both in an official sense, and in an implied sense, as the main intent of the present rules was actually to be comprehensive and avoid any lingering hidden rules or uncertain interpretations (as with the previous rules) so we can assume it's reasonably safe to engage in behaviors not explicitly prohibited within the rules (within the scope of common sense).

You could be banned

According to established site policies, you can only be banned if you harass staff while suspended. You can view suspension lengths at the bottom of this page; Inappropriate behavior, which calling out falls under, has only a base suspension length of 2 days (assuming it's not a new account which staff determines was created solely for the sake of disruptive behavior, in which case it could potentially receive a permanentindefinite suspension instead).

* I ran outta letters way too fast- sorry to anyone I didn't tag. :(

It's not just possible, it's 100% certain. Don't message them anything, the scammer will just block you and remove from friends so you lost a friend and gained nothing. Reporting it to Steam as compromised is the only thing that needs to be done. The original owner obviously knows that their account is stolen because they no longer have access to it so the only one you're alerting is the scammer.