This would be true.

They would have to work on the assumption that someone was inside, watching them, so they could plan an attack.

I would think this would be standard operating procedure, regardless of the reason they were there

Why wouldn't it work the other way? If the cops are present with overwhelming force, somebody who can SEE them coming is much less likely to resist, more likely to give up without a fight. Also less likely to think it's a bunch of burglars breaking in. In just about every movie ever, cutting off the surveillance video is something the BAD guys do - the GOOD guys know they're in the right so they shouldn't mind being seen.