I've deleted some or all of those apps from Miui on my SGS II and I have not get errors. I use Titanium backup to delete them but first create a backup of them, only for the case I need they later.
Enviado desde mi GT-I9100 usando Tapatalk
Contacts.apk showing phone info instead of icon (I have customised some info in phone numbers)
Calendar.apk with more features like in samsung rom
I know I can replace both apps but it would be great it came with the rom