Can a blu-ray DVD be played on an HD DVD player?

No. An HD DVD will only play on an HD DVD player. This format was released in competition with BluRay. It lost the battle after about one year and was withdrawn from sale. There are few HD DVD players and discs around and none have been made for a number of years.

the demise of the HD DVD video format should not come as a surprise when the two formats are compared and closely examined. First, the quality of both in terms of picture and sound are a huge step up from a regular DVD in resolution. However, when further investigating Blu-Ray, the storage capacity is four times greater than that of High Definition DVD. In my opinion, this is perhaps the largest deal breaker for High Definition DVD.

Unless the disc has some sentimental value, there is probably little point in retaining it.