We used those envelopes too. VERY CUTE.
However, both trips the housekeeper did not take them. On this Trip I caught her our second day, and made sue she knew it was for her. She thanked us, and stated, that she wasn't sure if she was suppossed to take it.
After that--I cut the end off the envelope, and stuck the end of the $$ out. Still looked cute, and no problems. They always took it.