Keloid scars are tough weirdly shaped scar that rises above the rest of the skin. It tends to enlarge progressively. These scars can develop over weeks and even months.
To answer your question, it can make keloid scars appear more red. This is due to the heat from the steam bath. It can cause dilation of the blood vessels within the scar.
However, it should not have any long term effects. Keloid scars are normally worsened if they are located in areas of increased movement. An example would be across joints.
Keloids can be effectively treated using a combination of VBEAM laser and steroid injections over a series of 4-5 monthly treatments.