Appropriate help request?

[insatty]

R3 breaks for home upon a slow chopper between F1 and 3B-HP baseline. F1 fields ball on the run toward R3 and attempts a tag on R3's back. PU on 1B-line extended can see that F1's glove is very close to R3's back but is screened from seeing a tag. After R3 crosses plate but before PU makes a call asks BU in position C, "Do you have a tag?" BU says "yes" and PU calls R3 out on the tag.

Is this an appropriate request for help in order to get the call correct or an absolute mechanical no-no?