Does my portal tell my customer whether breakfast is included in the room rate?

Yes, the room results on your portal show what the rate includes, and breakfast is one of the things called out there. Each room a hotel offers comes back to your portal as its own choice, and the same room is very often sold twice, once with meals and once without, so your customer picks the version they want rather than finding out at the hotel.

The wording your customer sees comes from the supplier, so it will not always read the same way from one hotel to the next. Some send back a clear line saying breakfast is included, some describe it as room only or as bed and breakfast, and a few describe a fuller board where lunch or dinner is covered as well. Your portal shows that line as it is given rather than rewriting it, because the hotel is the one honouring it at the front desk.

Be aware that a meal included in the rate is not the same as a meal already paid for at the hotel. Where a supplier only settles part of the stay directly, the hotel may still ask your customer to sign for the meal at the restaurant even though nothing more is owed. This is unusual, but it does happen with certain properties, so it is worth reading the room description in full rather than the short label alone.

When you are checking this, search a hotel you know well on your own portal and compare the room choices it returns against what that hotel actually sells, so you can see for yourself how the meal wording is coming through from the supplier you are on.