Using the Default or Material Kendo Theme (v5.6.0) with the Telerik HTML5 Report Viewer, the Boolean parameter which uses a Checkbox for it's display, is not visible (this may affect other themes as well).

I confirmed an older version v4.40.0 has a height and width set for the k-checkbox CSS class as such:

https://unpkg.com/@progress/kendo-theme-material@4.40.0/dist/all.css

.k-checkbox {
    border-radius: 2px;
    margin: 0;
    padding: 0;
    width: 16px;
    height: 16px;
    line-height: initial;
    border-width: 2px;
    border-style: solid;
    outline: 0;
    box-sizing: border-box;
    background-position: center;
    background-repeat: no-repeat;
    background-size: contain;
    display: inline-block;
    vertical-align: middle;
    position: relative;
    cursor: pointer;
    -webkit-appearance: none;
}

while the latest v5.6.0 does not:

https://unpkg.com/@progress/kendo-theme-material@5.6.0/dist/all.css

.k-checkbox {
    margin: 0;
    padding: 0;
    line-height: initial;
    border-width: 2px;
    border-style: solid;
    outline: 0;
    background-position: center;
    background-repeat: no-repeat;
    background-size: contain;
    display: inline-block;
    flex: none;
    vertical-align: middle;
    position: relative;
    cursor: pointer;
    -webkit-appearance: none;
}

The checkbox is actually on the page, but is so small it's basically invisible and completely unusable, requiring a manual CSS override to fix.