Depends on the amp design. Some amps have filaments wired in series, in which case obviously that approach won't work.
Otherwise, it might work obviously at reduced power and the plate tank circuit may not tune properly; but for just "idling" the tube to see if it fails with B+ applied, that should work fine.
Does the tester provide 2750Vdc for the anode? If it doesn't may not be much of a test, since when tubes arc internally, they often won't arc at reduced voltage, only at "full" voltage. I've seen lots of 572Bs that work fine at 1800V and fail at their normal operating voltage, which is around 2700V.
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