From Moore v. Vital Prods., Inc., 2009 U.S. Dist. LEXIS 7878 (N.D. Ill. Feb. 3, 2009):

First, there is nothing untoward about defendant offering affidavits from individuals who previously were deposed. A party is permitted to offer depositions as well as affidavits and/or declarations on summary judgment; these may be offered together, in isolation, or in any combination that will show the absence (or presence) of a genuine issue of material fact. A party may wish to offer an affidavit from a previously-deposed witness to fill in gaps on points not addressed in the deposition. Plaintiff cannot complain that he was not permitted to cross-examine statements because they appear by affidavit rather than in the deposition, since defendant is not under any obligation to elicit deposition testimony on topics plaintiff never explored when the affiant was deposed. To the extent that plaintiff deemed it necessary to depose certain affiants in order to file his opposition to this summary judgment motion, he could have filed a motion to do so pursuant to Federal Rule of Civil Procedure 56(f). ***

Of course, we agree that a party cannot seek (or resist) summary judgment with affidavits by persons that contradict their prior deposition testimony without explanation. See Kalis v. Colgate Palmolive Co., No. 95 C 7673, 1999 WL 417463, *2 (N.D. June 18, 1999), aff'd, 231 F.3d 1049, 1056 (7th Cir. 2000). But, here, we have not relied on any affidavit statements that contradict the affiants' prior deposition testimony. Thus, we are not persuaded that any conflict that exists is sufficient to strike the affidavits at issue.

Second, we reject the argument that the affidavits are "self-serving" simply because they are made by employees of the defendant and serve the interests of defendant. As the Seventh Circuit has commented, most affidavits submitted on summary judgment are, in that sense, self-serving…. Rule 56 does not require that affiants be independent from any party; it requires that affidavits "be made on personal knowledge, set out facts that would be admissible in evidence, and show that the affiant is competent to testify on the matters stated." Fed.R.Civ.P. 56(e)(1). In other words, the affiant must have an adequate foundation to offer the statements he or she makes.

[Need for Separate Representation When Sanctions Sought Against Both Client and Counsel; Practical Impediments.] Holding a sanction hearing as to both plaintiffs and their attorney, where the plaintiffs are not separately represented, is inherently problematic because of the conflict of interest presented. See In re Ruben, 825 F.2d 977, 985 (6th Cir. 1987) (noting the "inherent problem in a sanction hearing addressed to both a plaintiff and her attorneys, where the plaintiff and [the] attorneys are not separately represented," because the attorneys might abandon their client's interests during the hearing). But many civil rights plaintiffs might be able to retain an attorney only on a contingency basis, and requiring such plaintiffs to obtain an attorney to defend themselves against sanctions might be unrealistic. Although [counsel] Frost asserted during oral argument that she obtained her clients' informed consent to represent them on this appeal, we express no opinion on whether the applicable professional responsibility standards permit Frost to continue representing her clients in this matter. We leave the consideration of such representation issues to the district court on remand.