No, it is not at all poor form to query one VC with another. Just keep in mind the VC community works by excessive collusion, with uniform deal-intake criteria, deal fragmentation, and deal syndication to boot. Hence you may not get the real story from the VC, you know, for the sake of protecting the workings of the grand scheme of collusion and the protection of the role of the VC you see in it.
You should attempt to get feedback from other portfolio companies of the VC partner you do not know, especially from ones where the proverbial shit has hit the fan on their trajectory towards the upside. And see how the specific general partner acted when things did not ease. Personalities reveal themselves most when the going gets tough. Keep in mind the compass of the firm is secondary to the character of the general partner championing your deal, so be sure to include and discern between the two.
But all recommendations are highly susceptible to the interactions and personalities of both parties working together. To draw a corollary, you would never marry a person just because someone recommended that person (or not, save for flagrant reputation issues from a variety of sources that precede them). Remember, outlier entrepreneurs “marry” outlier general partners, so the opinion of the general public or entrepreneurs who are not outliers (there are many in subprime Lala-land) is not that relevant.
Hence, it is essential you interact with the unknown general partner of the VC firm on your own accord, and make up your mind as to how the two parties, yours and the VC firm, click on the alignment of foresight to help grow the proverbial baby (your startup) into an exemplary outlier adult.
My observation, having acted as a part-time venture partner on Sand Hill Road, is that a lot of VC firms continually test the waters of innovation without actually investing, sometimes for nefarious reasons. Like looking for new ideas derived from your pitch to unclog the performance of their current portfolio companies, or simply not having the financial runway to support upside from the current fund, or the general partner having sponsored the wrong ideas and becoming desperate, and sometimes dispensing ill-formed conclusions from your pitch unbeknownst to you to the rumor mill of the collusion above to other venture firms. So get to know the general partner before you decide to pitch.
Just because a firm calls themselves a venture firm does not mean they have the wherewithal, experience, or the merit to be your match. In general, I would suggest not to formally pitch, as I have so boldly refused in my past, without having 1:1 coffee a few times first and observing body language.